Yet there is a proposal - set old lclqt def inside qt5 widgeset code, many third-party packages are working fine after that.
It will be easier to solve some specific incompatibilities (e.g. with lazopenglcontext) than to have not working all third-party packages
Please test and close if ok. Note that this is OpenGL implementation with QWidget (as qt4 is implemented), I've already created QOpenGLWidget & QOpenGLWindow bindings and they're tested atm, so maybe, I'll change complete implementation for Qt5 opengl with native Qt5 OpenGL.
I can't reopen https://bugs.freepascal.org/view.php?id=34401
So I will write here. Why OpenGL QT5 support not merged to Lazarus 2.0 branch?
Though it's not quite right, but it's better than nothing