Bug (IN GAME)

Riot has found that discord overlays were at fault for players being unable to interact with the game, so if you use discord, try turning off your overlays.

If you don't use discord, or disabling the overlays doesn't work, try running League of Legends in administrator mode. You can do this by closing the game, right-clicking on it's icon, and selecting the "Run as Administrator" option.

You should also be careful about using any other additional apps or modifications, as they can be prone to causing issues, and they're not something Riot supports. You can read more about Riot's stance regarding this here: Third Party Applications.