Trail races are already pretty chill, but those looking to take low-key to an even lower level should go find a Fat Ass.
Fat Ass events are free, loosely organized group runs that focus on trail community and camaraderie over competition. Depending on the organizer, races will sometimes have aid, sometimes swag, and sometimes course markings, but an entry “fee” is always a donation of food or drinks to a communal aid station.