What exactly did I do:

1. First, I already had an existing Qt and QtCreator installation at "D:\Qt". This installation is managed by the Qt Maintenance Tool and resides in a write-protected directory.

2. I downloaded a fresh MSI installer from the latest GitHub release (see the link below) and ran through it with default settings. The installer created a directory under "C:\Program Files\".

https://github.com/qt-creator/qt-creator/releases/download/v16.0.0-beta1/qtcreator-windows-x64-msvc-16.0.0-beta1.msi

3. Then, I opened the newly installed QtCreator and went to "Edit — Preferences — Kits — Qt Versions". I added a couple of Qt versions manually and then noticed the "Link with Qt" button. So I pressed it and pointed it to my existing installation.

4. After I pressed "OK", the following error message appeared:

Title: Error Linking With Qt
Could not write to "C:/Program Files/qtcreator-15.0.82/share/qtcreator/QtProject/QtCreator.ini".

I should note here that the "QtProject" subdirectory does not even exist in the first place. And isn't it strange it tries to write anything into "Program Files" like it's still the 90s?