How do I force quit an app and turn off my iPhone X when it is stuck?

my phone is stuck on an app, it won't let me exit, it won't let me turn off my phone with the power button and I can't force shut it off by holding the phone's buttons. Even if I try to leave by using the notifications, it won't let me leave and I can't swipe out to leave (my phone is an iphone x)

[Re-Titled by Moderator]