Chosen Solution
This happens at a daily basis and it is not an overheating issue. Usually after 30 minutes of continuous use. For example, playing some PUBG mobile game, or watching a couple Youtube videos. The only way to get out of the temperature screen is hard reset or to wait it out.
Sounds like you have a hardware issue with your phone. Considering it is still under warranty, your best bet is to return it to Apple for an exchange. Make sure to back up your data first. The iPhone X has 4 thermistors to measure temperature at the forehead, rear camera, charge circuit and CPU. If one of those thermistors failed or if one of the modular components (camera) is drawing excess current, then it will trigger this warning message. There’s nothing you can do about this and having the logic board repaired doesn’t make sense at this point in time.
