He doesn't need to challenge the gyms, but nothing stop him to fight some of the leaders and/or the Team Star bosses.
He didn't battle the whole Galar gym set, but fought Bea, Opal and Raihan.
- Cues to Eri be an Ash fan and the only person in Paldea who watched the PWC (she started to train a lucario because of him).-
Go could investigate the Paradox 'mons and be suspect about the professors, assuming we have both professors.
Chloe can stay away, since Penny would be the obligatory eevee user. Also, it would be somewhat new the "evil team" boss be a companion.