Collaboration - with update I can't collaborate with the person I did before the update
I can't figure out how to add them to spreadsheets
iMac 24″, macOS 15.0
It is hard to know the specifics of your situation. But have you had a look at the support documents to make sure that you (and the other person) have set things up to (re)enable collaboration?
Intro to collaboration in Numbers - Apple Support
Collaborate on a shared spreadsheet in Numbers on Mac - Apple Support
It's possible that turning off any collaboration you had before and turning it back on again may help.
SG