We should not hide the performance metrics by default; this is the development build so I'd expect to see those.

For fullscreen; we can't use esc to exit it, people would likely use that to open the main menu. And if there's a button to exit it, there should also be a button to re-enter it.

Also whatever setting you switch to should be saved, so if I switch to windowed, it should keep that next time I launch ambient. I suspect a lot of people will still want to develop in windowed so just switching to fullscreen for everyone doesn't seem like a good idea.