You cannot build examples inside the Qt source tree, except as part of a proper Qt build.

C:\Users\ci\cxx\repos\test\my_proj\QtXlsxWriter\build\win32>"C:\Qt\5.14.2\msvc2017_64\bin\qmake.exe" -recursive ..\..
Info: creating stash file C:\Users\ci\cxx\repos\test\my_proj\QtXlsxWriter\build\win32\.qmake.stash
Info: creating cache file C:\Users\ci\cxx\repos\test\my_proj\QtXlsxWriter\build\win32\.qmake.cache
Reading C:/Users/ci/cxx/repos/test/my_proj/QtXlsxWriter/src/src.pro [C:/Users/ci/cxx/repos/test/my_proj/QtXlsxWriter/build/win32/src]
 Reading C:/Users/ci/cxx/repos/test/my_proj/QtXlsxWriter/src/xlsx/xlsx.pro [C:/Users/ci/cxx/repos/test/my_proj/QtXlsxWriter/build/win32/src/xlsx]
Project MESSAGE: perl -w C:\Qt\5.14.2\msvc2017_64\bin\syncqt.pl -module QtXlsx -version 0.3.0 -outdir C:/Users/ci/cxx/repos/test/my_proj/QtXlsxWriter/build/win32 -builddir C:/Users/ci/cxx/repos/test/my_proj/QtXlsxWriter/build/win32 C:/Users/ci/cxx/repos/test/my_proj/QtXlsxWriter
<srcbase> = C:/Users/ci/cxx/repos/test/my_proj/QtXlsxWriter
<bldbase> = C:/Users/ci/cxx/repos/test/my_proj/QtXlsxWriter/build/win32
<outbase> = C:/Users/ci/cxx/repos/test/my_proj/QtXlsxWriter/build/win32
QtXlsx: created fwd-include header(s) for <srcbase>/src/xlsx/ { xlsxabstractooxmlfile.h (1), xlsxabstractooxmlfile_p.h (1), xlsxabstractsheet.h (1), xlsxabstractsheet_p.h (1), xlsxcell.h (1), xlsxcell_p.h (1), xlsxcellformula.h (1), xlsxcellformula_p.h (1), xlsxcellrange.h (1), xlsxcellreference.h (1), xlsxchart.h (1), xlsxchart_p.h (1), xlsxchartsheet.h (1), xlsxchartsheet_p.h (1), xlsxcolor_p.h (1), xlsxconditionalformatting.h (1), xlsxconditionalformatting_p.h (1), xlsxcontenttypes_p.h (1), xlsxdatavalidation.h (1), xlsxdatavalidation_p.h (1), xlsxdocpropsapp_p.h (1), xlsxdocpropscore_p.h (1), xlsxdocument.h (1), xlsxdocument_p.h (1), xlsxdrawing_p.h (1), xlsxdrawinganchor_p.h (1), xlsxformat.h (1), xlsxformat_p.h (1), xlsxglobal.h (1), xlsxmediafile_p.h (1), xlsxnumformatparser_p.h (1), xlsxrelationships_p.h (1), xlsxrichstring.h (1), xlsxrichstring_p.h (1), xlsxsharedstrings_p.h (1), xlsxsimpleooxmlfile_p.h (1), xlsxstyles_p.h (1), xlsxtheme_p.h (1), xlsxutility_p.h (1), xlsxworkbook.h (1), xlsxworkbook_p.h (1), xlsxworksheet.h (1), xlsxworksheet_p.h (1), xlsxzipreader_p.h (1), xlsxzipwriter_p.h (1) }
QtXlsx: created version header
QtXlsx: created master header
QtXlsx: created headers.pri file
Reading C:/Users/ci/cxx/repos/test/my_proj/QtXlsxWriter/examples/examples.pro [C:/Users/ci/cxx/repos/test/my_proj/QtXlsxWriter/build/win32/examples]
 Reading C:/Users/ci/cxx/repos/test/my_proj/QtXlsxWriter/examples/xlsx/xlsx.pro [C:/Users/ci/cxx/repos/test/my_proj/QtXlsxWriter/build/win32/examples/xlsx]
Project ERROR: You cannot build examples inside the Qt source tree, except as part of a proper Qt build.

C:\Users\ci\cxx\repos\test\my_proj\QtXlsxWriter\build\win32>"C:\Qt\5.14.2\msvc2017_64\bin\qmake.exe" -recursive ..\..
Reading C:/Users/ci/cxx/repos/test/my_proj/QtXlsxWriter/src/src.pro [C:/Users/ci/cxx/repos/test/my_proj/QtXlsxWriter/build/win32/src]
 Reading C:/Users/ci/cxx/repos/test/my_proj/QtXlsxWriter/src/xlsx/xlsx.pro [C:/Users/ci/cxx/repos/test/my_proj/QtXlsxWriter/build/win32/src/xlsx]
Project MESSAGE: perl -w C:\Qt\5.14.2\msvc2017_64\bin\syncqt.pl -module QtXlsx -version 0.3.0 -outdir C:/Users/ci/cxx/repos/test/my_proj/QtXlsxWriter/build/win32 -builddir C:/Users/ci/cxx/repos/test/my_proj/QtXlsxWriter/build/win32 C:/Users/ci/cxx/repos/test/my_proj/QtXlsxWriter
<srcbase> = C:/Users/ci/cxx/repos/test/my_proj/QtXlsxWriter
<bldbase> = C:/Users/ci/cxx/repos/test/my_proj/QtXlsxWriter/build/win32
<outbase> = C:/Users/ci/cxx/repos/test/my_proj/QtXlsxWriter/build/win32
Reading C:/Users/ci/cxx/repos/test/my_proj/QtXlsxWriter/examples/examples.pro [C:/Users/ci/cxx/repos/test/my_proj/QtXlsxWriter/build/win32/examples]
 Reading C:/Users/ci/cxx/repos/test/my_proj/QtXlsxWriter/examples/xlsx/xlsx.pro [C:/Users/ci/cxx/repos/test/my_proj/QtXlsxWriter/build/win32/examples/xlsx]
  Reading C:/Users/ci/cxx/repos/test/my_proj/QtXlsxWriter/examples/xlsx/hello/hello.pro [C:/Users/ci/cxx/repos/test/my_proj/QtXlsxWriter/build/win32/examples/xlsx/hello]
  Reading C:/Users/ci/cxx/repos/test/my_proj/QtXlsxWriter/examples/xlsx/extractdata/extractdata.pro [C:/Users/ci/cxx/repos/test/my_proj/QtXlsxWriter/build/win32/examples/xlsx/extractdata]
  Reading C:/Users/ci/cxx/repos/test/my_proj/QtXlsxWriter/examples/xlsx/style/style.pro [C:/Users/ci/cxx/repos/test/my_proj/QtXlsxWriter/build/win32/examples/xlsx/style]
  Reading C:/Users/ci/cxx/repos/test/my_proj/QtXlsxWriter/examples/xlsx/documentproperty/documentproperty.pro [C:/Users/ci/cxx/repos/test/my_proj/QtXlsxWriter/build/win32/examples/xlsx/documentproperty]
  Reading C:/Users/ci/cxx/repos/test/my_proj/QtXlsxWriter/examples/xlsx/image/image.pro [C:/Users/ci/cxx/repos/test/my_proj/QtXlsxWriter/build/win32/examples/xlsx/image]
  Reading C:/Users/ci/cxx/repos/test/my_proj/QtXlsxWriter/examples/xlsx/mergecells/mergecells.pro [C:/Users/ci/cxx/repos/test/my_proj/QtXlsxWriter/build/win32/examples/xlsx/mergecells]
  Reading C:/Users/ci/cxx/repos/test/my_proj/QtXlsxWriter/examples/xlsx/rowcolumn/rowcolumn.pro [C:/Users/ci/cxx/repos/test/my_proj/QtXlsxWriter/build/win32/examples/xlsx/rowcolumn]
  Reading C:/Users/ci/cxx/repos/test/my_proj/QtXlsxWriter/examples/xlsx/numberformat/numberformat.pro [C:/Users/ci/cxx/repos/test/my_proj/QtXlsxWriter/build/win32/examples/xlsx/numberformat]
  Reading C:/Users/ci/cxx/repos/test/my_proj/QtXlsxWriter/examples/xlsx/datavalidation/datavalidation.pro [C:/Users/ci/cxx/repos/test/my_proj/QtXlsxWriter/build/win32/examples/xlsx/datavalidation]
  Reading C:/Users/ci/cxx/repos/test/my_proj/QtXlsxWriter/examples/xlsx/definename/definename.pro [C:/Users/ci/cxx/repos/test/my_proj/QtXlsxWriter/build/win32/examples/xlsx/definename]
  Reading C:/Users/ci/cxx/repos/test/my_proj/QtXlsxWriter/examples/xlsx/formulas/formulas.pro [C:/Users/ci/cxx/repos/test/my_proj/QtXlsxWriter/build/win32/examples/xlsx/formulas]
  Reading C:/Users/ci/cxx/repos/test/my_proj/QtXlsxWriter/examples/xlsx/richtext/richtext.pro [C:/Users/ci/cxx/repos/test/my_proj/QtXlsxWriter/build/win32/examples/xlsx/richtext]
  Reading C:/Users/ci/cxx/repos/test/my_proj/QtXlsxWriter/examples/xlsx/conditionalformatting/conditionalformatting.pro [C:/Users/ci/cxx/repos/test/my_proj/QtXlsxWriter/build/win32/examples/xlsx/conditionalformatting]
  Reading C:/Users/ci/cxx/repos/test/my_proj/QtXlsxWriter/examples/xlsx/worksheetoperations/worksheetoperations.pro [C:/Users/ci/cxx/repos/test/my_proj/QtXlsxWriter/build/win32/examples/xlsx/worksheetoperations]
  Reading C:/Users/ci/cxx/repos/test/my_proj/QtXlsxWriter/examples/xlsx/hyperlinks/hyperlinks.pro [C:/Users/ci/cxx/repos/test/my_proj/QtXlsxWriter/build/win32/examples/xlsx/hyperlinks]
  Reading C:/Users/ci/cxx/repos/test/my_proj/QtXlsxWriter/examples/xlsx/chart/chart.pro [C:/Users/ci/cxx/repos/test/my_proj/QtXlsxWriter/build/win32/examples/xlsx/chart]
  Reading C:/Users/ci/cxx/repos/test/my_proj/QtXlsxWriter/examples/xlsx/chartsheet/chartsheet.pro [C:/Users/ci/cxx/repos/test/my_proj/QtXlsxWriter/build/win32/examples/xlsx/chartsheet]
  Reading C:/Users/ci/cxx/repos/test/my_proj/QtXlsxWriter/examples/xlsx/calendar/calendar.pro [C:/Users/ci/cxx/repos/test/my_proj/QtXlsxWriter/build/win32/examples/xlsx/calendar]
  Reading C:/Users/ci/cxx/repos/test/my_proj/QtXlsxWriter/examples/xlsx/demo/demo.pro [C:/Users/ci/cxx/repos/test/my_proj/QtXlsxWriter/build/win32/examples/xlsx/demo]
  Reading C:/Users/ci/cxx/repos/test/my_proj/QtXlsxWriter/examples/xlsx/xlsxwidget/xlsxwidget.pro [C:/Users/ci/cxx/repos/test/my_proj/QtXlsxWriter/build/win32/examples/xlsx/xlsxwidget]
Reading C:/Users/ci/cxx/repos/test/my_proj/QtXlsxWriter/tests/tests.pro [C:/Users/ci/cxx/repos/test/my_proj/QtXlsxWriter/build/win32/tests]
 Reading C:/Users/ci/cxx/repos/test/my_proj/QtXlsxWriter/tests/auto/auto.pro [C:/Users/ci/cxx/repos/test/my_proj/QtXlsxWriter/build/win32/tests/auto]
  Reading C:/Users/ci/cxx/repos/test/my_proj/QtXlsxWriter/tests/auto/utility/utility.pro [C:/Users/ci/cxx/repos/test/my_proj/QtXlsxWriter/build/win32/tests/auto/utility]
  Reading C:/Users/ci/cxx/repos/test/my_proj/QtXlsxWriter/tests/auto/worksheet/worksheet.pro [C:/Users/ci/cxx/repos/test/my_proj/QtXlsxWriter/build/win32/tests/auto/worksheet]
  Reading C:/Users/ci/cxx/repos/test/my_proj/QtXlsxWriter/tests/auto/zipreader/zipreader.pro [C:/Users/ci/cxx/repos/test/my_proj/QtXlsxWriter/build/win32/tests/auto/zipreader]
  Reading C:/Users/ci/cxx/repos/test/my_proj/QtXlsxWriter/tests/auto/relationships/relationships.pro [C:/Users/ci/cxx/repos/test/my_proj/QtXlsxWriter/build/win32/tests/auto/relationships]
  Reading C:/Users/ci/cxx/repos/test/my_proj/QtXlsxWriter/tests/auto/propscore/propscore.pro [C:/Users/ci/cxx/repos/test/my_proj/QtXlsxWriter/build/win32/tests/auto/propscore]
  Reading C:/Users/ci/cxx/repos/test/my_proj/QtXlsxWriter/tests/auto/propsapp/propsapp.pro [C:/Users/ci/cxx/repos/test/my_proj/QtXlsxWriter/build/win32/tests/auto/propsapp]
  Reading C:/Users/ci/cxx/repos/test/my_proj/QtXlsxWriter/tests/auto/document/document.pro [C:/Users/ci/cxx/repos/test/my_proj/QtXlsxWriter/build/win32/tests/auto/document]
  Reading C:/Users/ci/cxx/repos/test/my_proj/QtXlsxWriter/tests/auto/sharedstrings/sharedstrings.pro [C:/Users/ci/cxx/repos/test/my_proj/QtXlsxWriter/build/win32/tests/auto/sharedstrings]
  Reading C:/Users/ci/cxx/repos/test/my_proj/QtXlsxWriter/tests/auto/styles/styles.pro [C:/Users/ci/cxx/repos/test/my_proj/QtXlsxWriter/build/win32/tests/auto/styles]
  Reading C:/Users/ci/cxx/repos/test/my_proj/QtXlsxWriter/tests/auto/format/format.pro [C:/Users/ci/cxx/repos/test/my_proj/QtXlsxWriter/build/win32/tests/auto/format]
  Reading C:/Users/ci/cxx/repos/test/my_proj/QtXlsxWriter/tests/auto/richstring/richstring.pro [C:/Users/ci/cxx/repos/test/my_proj/QtXlsxWriter/build/win32/tests/auto/richstring]
  Reading C:/Users/ci/cxx/repos/test/my_proj/QtXlsxWriter/tests/auto/xlsxconditionalformatting/xlsxconditionalformatting.pro [C:/Users/ci/cxx/repos/test/my_proj/QtXlsxWriter/build/win32/tests/auto/xlsxconditionalformatting]
  Reading C:/Users/ci/cxx/repos/test/my_proj/QtXlsxWriter/tests/auto/cellreference/cellreference.pro [C:/Users/ci/cxx/repos/test/my_proj/QtXlsxWriter/build/win32/tests/auto/cellreference]
  Reading C:/Users/ci/cxx/repos/test/my_proj/QtXlsxWriter/tests/auto/cmake/cmake.pro [C:/Users/ci/cxx/repos/test/my_proj/QtXlsxWriter/build/win32/tests/auto/cmake]