Can't add Qt versions in 'Qt versions' wizard when using 'Qt vs tools'

[diverger]

I'm using VS 16.9.5 with Qt vs tools 2.7.1 (rev. 18). After adding the Qt's qmake.exe path in 'Qt versions' wizard, and pressing OK. The the 'Qt VS Tools' output to the VS output window some error messages:

--- qmake(5544): started E:\QT\OFFICIAL\5.15.2\MSVC2019\bin\qmake.exe
--- qmake: Querying persistent properties
--- qmake(5544): exit code 0 (92.02 msecs)

--- qmake(10984): started E:\QT\OFFICIAL\5.15.2\MSVC2019\bin\qmake.exe
--- qmake: Working Directory: C:\Users\diver\AppData\Local\Temp\sttjxfga.23c
--- qmake: Arguments: QMAKE_INCDIR_QT=$(QTDIR)\include QMAKE_LIBDIR=$(QTDIR)\lib QMAKE_MOC=$(QTDIR)\bin\moc.exe QMAKE_QMAKE=$(QTDIR)\bin\qmake.exe -o "sttjxfga.23c.vcxproj" -tp vc -Wnone "sttjxfga.23c.pro"
Info: creating stash file C:\Users\diver\AppData\Local\Temp\sttjxfga.23c.qmake.stash
Project ERROR: msvc-version.conf loaded but QMAKE_MSC_VER isn't set
--- qmake(10984): exit code 3 (295.35 msecs)

Error reading VS project settings

Stacktrace:
at QtVsTools.Core.VersionInformation..ctor(String qtDirIn)
at QtVsTools.Core.VersionInformation.Get(String qtDir)
at QtVsTools.Options.QtVersionsPage.SaveSettingsToStorage()
--- qmake(18544): started E:\QT\OFFICIAL\5.15.2\MSVC2019\bin\qmake.exe
--- qmake: Querying persistent properties
--- qmake(18544): exit code 0 (58.39 msecs)

So, actually the Qt version is not be added. When I open the wizard again, the versions are empty again.

I've reported this to VS tools guys. But had no replies for about months. So, I come here for help.

Thanks.