You can go to the SteamDB page for a game, click App Info on the left, then look for the “Detected Technologies”. This will usually tell you what they’re using if it’s not a custom engine. You can use the Augmented Steam or SteamDB browser extensions to get a direct link to the SteamDB page from a game’s store page.

Also, SteamDB has a page here with aggregate data of how much each detected engine is used across Steam. Unity currently accounts for over half of the games using known engines (snapshot).

Edit: For non-Steam games you could check out IGDB.com. It has crowd-sourced data on all video games, including which game engine was used.

Team Fortress 2 and Fall Guys have this quality as well. I wish more games would embrace the goofiness. It’s harder to take a match so seriously as to become toxic when the game isn’t even taking itself seriously.