iPhone 12 Pro, could someone be mirroring my phone?

Ip12 pro, updated to current version, though it has been getting extremely hot to the touch at random times, with a full battery or more than half, it will suddenly slow down when texting, suddenly start loading with the load icon appearing center screen and keep moving around ,, battery dies often and quick, seems that my messages get lost bc once I notice it appears that they’ve already been checked, & so on!

I know of an app that I came across a couple years back that you could purchase something from this site and once you got it , you could spy on someone’s phone. I’m not sure as to what it was now, but with apple I know they pride in their security but with there being known ways made to spy on others, I would love to know how to find out if someone has been or is spying and/or how to remove any ways of future effort in doing so while also blocking and removing whomever it could be,,, also extra steps in making sure it doesn’t happen.

I have 2 step, & every other way to stay safe but seems no matter what I do, I still have issues.

for instance, what if it could be from a shopping app, since so many are across seas, china, etc., and that’s how my phone/ phones in general are being looked at! What are ways to also prevent & remove,, again I have set up all initiatives to prevent but seems there’s still a way for it to happen.

Thanks so much, for any replies, trying to help.