Giving old PC to a friend, not Win11 capable

Sorry if this kind of question gets asked a lot, but I had done a cursory search and couldn't find an answer that fit.

I'm giving my old PC to a friend that has a i5-6600K and GTX 1060. What I would change in it is the PSU and install new HDD and SSD. If I changed the drives out, obviously I would need to do a fresh install of Win10, but would I have to find my current activation key, or would his microsoft acct work for that? I would rather not buy a sketchy key off a reseller, can't upgrade it to Win11, and he isn't up for the linux switch.

Any advice would be greatly appreciated.