Valve announced a change for Steam today that will make things a lot clearer for everyone, as developers will now need to clearly list the kernel-level anti-cheat used on Steam store pages.
Now if only they could more clearly communicate when games are playable offline.
Valve was giving refund when riot added the anticheat
Are there Riot games on Steam?
They publish their single player games to steam. Don’t know about any of their multiplayer ones though.
I believe those are games made by other studios with the League IP and published by Riot. AFAIK there’s no reason for them to have anticheat.