iOS 17 is supposed to come with a new "Assistive Access" setting[0] which is intended to be an "old person's mode" with limited but pronounced functionality.

In the meantime, you should be able to solve the call banner issue through a relatively hidden setting; Settings > Phone > Incoming Calls > "Full Screen" should put things back to the way they were.

[0] https://www.apple.com/newsroom/2023/05/apple-previews-live-s...