What do people who use XTR cable kit use at the cable stop at the derailleur?
The shimano instructions are a little wooly, only a statement if you are getting a lot of movement, like on a full suss, use the metal ferrule. It’s not clear if in the opposite situation you should use the plastic ferrule or the cable shield.
I’m running full outers so the derailleur is the only point that dirt could enter the outer.

Ferrule. The shield probably won’t even fit in the hole in the mech, as it’s designed for just an inner. Didn’t on older mechs certainly.