iPhone feeling warm, despite no apparent issues?

I took my iPhone 12 Pro to an Apple Store the other day to fix an issue with my charging port. Then, they ran diagnostics and all the boxes were green, so my phone should be running perfectly right?

Unfortunately, for some reason my phone gets warm when I use it, even if I only have two apps open. I give it to other people to see if it’s just me, but they say that “it’s normal” but before it never got that warm.

Also, not sure if this other issue is connected, but when my phone reaches 90% battery when charging it takes a while before getting to 100%, even on airplane mode. Again, something that didn’t happen until recently.

I dunno if it’s a bug or something, but one of the solutions I read is resetting the iPhone, but I’m afraid of deleting stuff off this thing even if I have it backed up. Any advice?