Same problem on my VS 2019...
I erased the directory %QtMsBuild% (on my Windows %USERPROFILE%\AppData\Local\QtMsBuild) and the error disappeared.
However, I now have Linker-Errors like LNK2001 on MyClass::qt_metacall(enum QMetaObject::Call,int,void * *)
Sounds like something's wrong with Qts MOC. See you maybe later for updates.