You updated to the new public release or to the new beta?
I’ve got same device as you and haven’t had the same issues.
I’ve got same device as you and haven’t had the same issues.
I was never on the beta.
What you describe is exactly what I've experienced on more than one iPhone when the battery failed... but yeah, good luck convincing them to swap it out under warranty if they're certain that's not the problem.
Regardless, the device overheating to this extent is a serious issue regardless of what causes it. It’s on Apple to make sure they design safe hardware and responsibly release working software.