Hey there,
I have been trying to install Legends of Runeterra (it just came out, so there's nothing in the AppDB yet). The install runs perfectly, and runs the launcher app. Once I click to have the launcher run the actual game, it says there was an error. It's an in-app error, so it just says "Something unusual happened while trying to launch".
I'm still running Mojave, and happy to answer any questions/provide logs.