My Steam Deck had the loud whining fan, and noticed temperature issues.
Repair went great, this has been the easiest repair I've done in awhile. I used to repair several iPhones and this was a piece of cake in comparison.
Definitely read the ifixit guide and carefully follow the steps they show. Take your time with it and have fun. The main advice I have is to be extra gentle with the small fan power connector. Its so tiny and there were times i felt like I would break it but in the end it went well. The new fan is absolutely amazing, i barely hear it while playing more intensive games. This repair was definitely worth it.