To troubleshhot thi with extensions off would answer this question:
Do you have "Bartender" enabled as a third party xtension or cntrl panl?
Bartender makes the menubar disappear. If someone installed it, that could be it.
If restarting with xtensions off helps, it is definetly an xtension.
If you don't se a bartender like xtension or cntrl panel, you may need to do the old reboot with half then a quarter, then less & less xtensions until the problem goes away or you only have one xtension left.
You'll find the culprit unless it has nothing to do with xtensions, which is IMHO highly unlikely.
Also search the TIL at apple's web site.