[Solved] Claws Email: show/hide menu bar

[Second Round]

Supposedly, ctrl+F12 will toggle the menu bar in and out of view. However, on my Linux Mint machine (Linux Mint 19.3 Tricia x86_64), unchecking it (with the mouse: View, show/hide menu bar) hid it, but the ctrl+F12 won't bring it back. Can anyone help? Is there something in a config file that can be edited? Thanks.

What I've tried:

A different keyboard (for which ctrl-F12 does work to toggle the menu bar under Raspberry Pi OS)
I didn't find anything relevant in my computer's BIOS, regarding the function keys.
Nor under LM's "Settings | Keyboard".

SOLUTION:
Go into Window Manager, Keyboard Tab.
Scroll down to Workplace 12 under "Action" column.
Click "Edit" button
Click "X" button
Close Window Manager

So basically it looks like a conflict between default key bindings under xfce and keyboard shortcuts used by Claws Mail. It is unfortunate that you can use your mouse to hide the menu bar but there's nothing you can do with the mouse to get it back.