hm...registerEventNotifier() is not mentioned in obsoleted functions, it seem that they removed it in Qt6 without notice.
Just comment QAbstractEventDispatcher_registerEventNotifier and QAbstractEventDispatcher_unRegisterEventNotifier in qabstracteventdispatcher_c.cpp and qabstracteventdispatcher_c.h. I haven't tried build Qt6Pas.dll for windows yet, so pls if you spot any other errors beside this just let me know. If it builds w/o problems, I'll comment those routines and commit.