@shraga100 hmm your options are fairly limited out of the box, unfortunately.
The Google SSO plugin is pre-populating the usernames upon registration mostly as a convenience measure, so the name is recognizable (and most times, what they want to show).
Of course that's not always going to be the case, and especially in situations where you have username changes turned off, that could be problematic.
A possible solution here would be to write an additional feature to the Google SSO plugin (or perhaps a separate plugin) that would introduce an registration interstitial to prompt for a username change, but it seems pretty niche, to be honest.