The Qt Installer only supplies binaries for VS2015 and VS2019. It has been stated that VS2017 and VS2019 are binary compatible, and so no pre-compiled binaries for VS2017 are required anymore (e.g.
But most Qt Debug DLLs (e.g. "Qt5Cored.dll") now depend on "VCRUNTIME140_1D.dll", which appears to be part of the VS2019 debug runtime and is not available if no VS2019 is installed.
So even though it is still possible to compile Qt applications in debug configuration with VS2017, it seems to be impossible to actually execute them.
Curiously, the x86 Qt DLLs do not depend on VCRUNTIME140_1D and can therefore be used just fine with VS2017.
Find attached two Dependency Walker screenshots showing the dependencies of Qt5Cored.dll in both x86 and x64 configuration.