I'm doing 4-5 times/week 2 or 3 set, but I don't have a fixed schema.
One day I do first set to failure, second and thirtd sets 10 reps or second set to 10 reps and third set weight partial
Other day maybe I do weight pull up to 8 failure, then I drop weight and do a second set to failure two.
So many times I do 3x10
P.S: I do only extrict pull ups