I had a had a displaced radius head fracture in March this year. Operated on and plate and pins inserted. Was back on the bike within a couple of months.
Still have stiffness (especially in the cold) and it hurts to do press ups with palms flat on floor but it hasn’t stopped me doing anything.
I don’t mountain bike, but have taken the gravel bike on some red runs (Cannock and Sherwood so nothing too gnar) and that was OK – helped by Redshift stem.
Good luck with recovery.