By default qtquickcompiler is enabled in "build settings" of a new project, so "CONFIG += qtquickcompiler" is automatically added to "Effective qmake call"
It is expected that this line in project *.pro file:

CONFIG -= qtquickcompiler

should override the value, but it doesn't work. The value is read from and saved to *.user instead.

Since qtquickcompiler is broken in 6.3 and 6.4 for multi-project configurations, it would make sense to disable it by default.