Yeah I noticed this too going from 14.2 to 14.3, but thought it was just me or maybe this happens sometimes and its normal. I have not tried 14.3.1 yet. It’s really awful when the autocomplete isn’t working. I downgraded to 14.2 which has/had been OK for me.
I feel like macOS works better if I wait a bit longer to update, and if I monitor that things are working correctly after each change. With linux (Debian) I could update and/or upgrade quickly and often, and didn’t have to worry about it quite as much.
Just a heads up, I submitted a bug report and they seemed to have fixed this in Xcode 15 beta 5.
So I would recommend Xcode 15 when it comes out or stick with Xcode 14.1 or 14.2 from the links above.