Just reporting this in case anyone else has the issue or there's a fix.
I have a newly setup Pixel 7 Pro. The main / default user profile works great as is. Profile 1.
I've setup 2 additional users and both initially work, but as I add applications they stop responding to scrolling gestures and have only a black screen with a white bar in the centre at the bottom when I close an app.
If I turn off and then log in again, I can see the home screen and launch an application on it, but if I gesture to move to another application, the black screen happens.
I read maybe the apps were looking for Google service, which I installed on profile 2. It didn't make any difference initially.
On Profile 2, I found that when I changed System > Gestures > 3 button navigation, it all worked again.
The odd thing is when I change it back to > Gesture Navigation after this, it works again ... at least for now.
Maybe unrelated, but I then tested it in Profile 2, and Gesture Navigation is working although I understand this profile is unrelated to Profile 3 settings, so it could just be a coincidence.
I can't find anything anywhere on this issue, but am happy to be pointed there if I missed it. If a log or something is needed, and someone can point me at how to generate and where to put it, I'm happy to do that.
While I'm here ... thanks to the Devs who make this possible. Very grateful for your efforts. Graphene is fantastic and f_ck not just Google, but everyone tracking me.