Adding Non Steam Games in SteamPlay

There has always been a feature in Steam to add non-Steam games.

https://streamable.com/pukwz

For example retail or downloaded games like:

• Unreal Tournament 3
• Doom 3
• Quake Wars
• Indie Games
• MMORPGs

But not it appears SteamPlay supports this feature as well. Add a non-Steam game and select a version of Proton.

This could totally put PlayOnLinux and Lutris out-of-business