My understanding is big schools offer recruits an upfront NIL guarantee which is a fig leaf for a salary. South Carolina's has been made public. A group of lawyers gives ea signee 25K, not sure if it's lump sum, payed monthly, etc. In return, the group may ask the athlete to make a commercial, a tik tok, sign tshirts, etc. at some point in the future. Reportedly this is the part the LVs were struggling to find donors for. There is reluctance to sink big money into an unproven high school player. More willing to pony up for a proven portal player.
Athletes are free to also pursue actual name, image and likeness the way it was intended where they do events, sell jerseys, etc and get a cut of the proceeds.