Sorry for the late reply. I found a solution for myself that works perfectly fine. I use AirVPN WireGuard configs with this windows client: https://github.com/TunnlTo
It has split-tunneling per ip/app-name/folder. I just excluded the whole Riot Folder ( c:/Riot Games) and than the game starts perfectly fine with AirVPN enabled, since the whole folder and everything inside runs outside of the tunnel.
Hope i could help
-kind regards