Find And Replace not working in Numbers, how to fix?

Back in your account, the first action is to go to System Settings / General / Login Items and make a list of what you see (to be able to put them back after). Then either you remove them all at once or one at a time and restart the computer each time (since it only affects your account maybe just logging out and in would do too but let's be sure, if you're patient). If you're lucky you will finally be able to identify a culprit (or more complicated, a combination). You can also think about all those extra non-Apple items on the right of your menu bar, try deactivating them to see what happens. Do you also have custom keyboard shortcuts?

If that doesn't work, then a hidden process is at play. You can try starting the computer in safe mode, see Start up your Mac in safe mode - Apple Support. However, this will not really help in finding where is the problem exactly.

I'm wondering if you have had time to do a bit of troubleshooting. Any discovery?

I assume this problem is present in all your Numbers files, even simple ones, right?

Also, have you seen these problems:

• the search box problem affects other programs like TextEdit, Notes, Pages, Keynote
• you are unable to type text in Numbers' headers and footers (in the print preview)

Considering the number of people reporting this but the inability of anyone to pinpoint a definitive source can you help run a small experiment? It doesn't happen to most people including me so I think it may be interference from other software.

Can you create a temporary account on your computer and leave it as virgin as possible, just as MacOs creates it? Don't change any system settings, don't add anything, don't even connect your iCloud account. Then run Numbers and see if the same problem occurs. Thank you for your cooperation.