League of legends currently works without issue on performance level 2, but not performance level 3.
On performance level 3 League of Legends complains that you are using an "unsupported operating system" but Level 2 and level 3 use the same OS and level 2 works fine. It is a bug with the game's anti-cheat which has a list of supported CPU models. Level 2's CPU is included in this approved list by Riot, but Riot is working on adding the newer CPU used in performance level 3.
While it works fine out of the box on Performance level 2, you can get it to work on Level 3 with this trick (until this issue is patched by riot):
On Stim.io Performance Level 3, Inside of League of Legends:
"Head to profile > Ranked tab > click the yellow question mark on top left beside the text Queue up from there and you'll be fine. Another solution is to just ask a friend to invite you to a lobby, you'd be able to find games from that point on." - Above Trick From Reddit: https://www.reddit.com/r/riotgames/comments/1atf7ew/says_unsupported_system_but_i_have_windows_11/