My iPhone keeps randomly shutting off

Hello everyone,

So my issue is I have an iPhone 13 that is fully updated. The issue started about a week ago but it’s been hard to fix as I am currently over seas. I was about to use my phone after putting it down about 20 minutes earlier and it would turn on. Naturally, I put it to charge but it didn’t turn on till randomly about 9 hours later. It’s been happening pretty much everyday. Sometimes when it turns on it shows like a white screen that says something about needing to recover? But other times it just brings me to the login screen. I just got my phone on again after it being turned off for over a day. I called apple and they said it may be a hardware issue but they can’t fully diagnosed as I’m not in person. Does anyone have any tips? Anything will help. Thank you!!!!