Tools > Preference > Advanced > Shortcuts > Keyboard
setup > Choose the one you are using > Edit > Search for
"F11"
You should see two entries, "F11 ctrl" and "Platform Unix, F11
alt". Remove the "Platform Unix, " text and save your settings. You
should be able to hide the menu bar by pressing Alt+F11 now. Let me
know if you still can't figure it out; I have some screenshots here
which I'm kinda lazy to upload now.