Keyboard keys 1 to 9 are not working on the built-in keyboard

I would first try and external keyboard to see if row 1-9 works. If it does, then make sure that the keyboard connector is in good shape and is making a good contact with the motherboard connector. Maybe even clean the contacts with contact cleaner. It could be that Catalina has reserved those keys for other functions or that you may need to access keyboard configuration and see if there is any option to change the keyboard’s layout or some other option within. It might be that you have to do a combination of keys, such as OPTION key, COMMAND key, CONTROL key or even SHIFT key + #NUMBER#. Try all combinations. Otherwise, you could try to install the latest good known version of OSX into an external drive and boot from that drive holding OPTION key while booting. A menu will appear as follows:

If that solves the issue, then the problem lies within Catalina, otherwise, the keyboard connector at some point of one of it’s tracks has been severed from the row from 1 - 9 and you must change the connector cable or fix it (which is not easy) or use an external keyboard for now.

I hope this helps and please let us know how it went! :)