Please see Bereishis 50:21. I heard it said that Yosef never actually forgave them with the word Mochel. His words appear to show that no ill feeling remained inside him. What’s the significance of the word Mochel? Is it linked with the 10 martyrs? What practical difference would mechila have made?
Rabeinu Bachya in Bereishis 50-17 says it. From What he says there it seems that the word mochel means, that they are no longer responsible for what they did and not Yosef is carrying that burden, or that issue himself.