How do I auto forward all text messages from my work iPhone 8 to my personal iPhone X

While you can't autoforward to another iPhone, you could do so to your Mac or iPad or iPod: https://support.apple.com/en-us/HT208386 or you can manually forward with the more option. In addition this years iPhone lineup has the dual sim feature that may benefit you when you look to upgrade.

There is no auto forward for text messages.

If they get a modicum of text messages each day that is going to become very cumbersome.

Unless they wanted their personal and work phone number on one work phone (not a good idea) that will not help them.

While I agree it would be cumbersome, it is an option if something is needed on both devices, which is why I included it. I have to do it on mine, and while not fun (because its time consuming if you have to forward a lot) its easy.