iphone X won't login to Pokemon Go

You could try Force Restarting How to force restart the iPhone X - iFixit

If that doesn’t work the try deleting the App and then redownload again from the App Store.

This site might help https://www.unlockboot.com/fix-pokemon-go-crashing-on-startup-on-iphone/

The only other thought, the sign in page gives three options to use, via Trainer, Google or Facebook, have you tried a different way to normal.