Arrow key is not working in Messages app in Big Sur when the app is on the second screen

To make this even more obscure: Not only does this only happen on the second screen. Also: If you turn off the system preference “Keyboard→Shortcuts→Use keyboard navigation to move focus between controls” this is also “fixed” on the second screen, even though that preference should only affect the behaviour of the tab key and not the arrow keys.

Another thing: Shift-Arrow does not select the text in Messages anymore. And that is always broken, also on the first screen or with the setting above. Hopefully this is fixed in the next update.

So far I'm not experiencing the first issue you described (not being able to use the arrows on the second screen), but I am experiencing the second one: Shift-Arrow doesn't select the text in Messages. As far as I can tell, this is only happening in Messages.

Hmm, thanks for making me check. Option-arrow works to skip words, and option-shift-arrow works to select whole words. But still not shift-arrow. Option-shift-arrow would have to serve as a workaround until (unless?) they fix the shift-arrow bug.

Also, option + arrow still works to skip entire works? Really weird bug this

I am experiencing the same problem in messages. Shift arrow works fine in all other apps, including 3rd party.