I don't have trouble with Qt5 on linux:
install Qt5 packages
make sure you run "make distclean; rm -rf generated", if you are switching between Qt4 and 5.
We need linux users who can figure out how to build LibreCAD using Qt 5.
Supporting Qt 4 is preventing us from fully utilizing Qt 5 features.
If you figure it out, then please note the required steps.