Unable to use excel on my mac os

If a simple reboot of your Mac doesn’t fix things, see if the problem still happens in Safe mode. It can take much longer to safe boot (5 min) so be patient.

How to use safe mode on your Mac - Apple Support 

Safe mode will often correct weird software behavior by forcing the OS to do cache clearing and other housekeeping. When you're in safe boot, the machine won’t be at its best performance, especially with graphics, but that's expected.

Does the problem persist while in Safe mode?

Exit safe mode by restarting your Mac normally and evaluate the issue again.

Fix for 789uiojkl keys or numeric keypad … - Apple Community

Are you keying those numerals via the number keys above the letters on the keyboard, or do you have an extended keyboard with a 10 key on the side?