They've been doing plenty of League side games.
https://store.steampowered.com/search/?category1=998&supportedlang=english&publisher=Riot+Forge
Looks like they are all from different developers though, so they must be licencing out their IP. I had only heard of 2 of them. Huh there's even an Ekko game, I had no idea.
Riot really should promote these League games better.