Technically this is because a lot of apps thumb their nose at the requirement to have safe areas around swipeable elements in their app, but as a user, that is not my problem to fix. It's Google's.
The workaround is so ridiculously easy too: only allow backswipes to count in the lowest 15% of the bottom left of the screen. Yet despite having hundreds of engineers earning ±350.000 per year work on this problem for years, they haven't been able to either implement or even think of it.
The real fix would be to deprecate the three button layout in Android 18 and remove it in Android 19. Force apps to comply.