That's what I meant.

I followed my own build instructions from the README. You did it the exact same way I did.
@KevinH : it acts for all the world like something is different with QWebEnginePage::InsertUnorderedList() and QWebEnginePage::InsertOrderedList() for that particular Qt5.12.8 on that system. Weird. Maybe it was always there on Linux in 5.12.8. Arch (which is what I would have been testing with) had moved on to 5.13 and 5.14 before 5.12.8 was ever released.