You can already do that
chess.com add this!!!

Click on "Custom Game", and turn off the toggle that says "Rated"
If you aren't playing a friend, it could take a while to find an opponent, though

oh ok
You've been on this site for a year and a half. I'm surprised you didn't know this yet.
By the way, the Bongcloud is undoubtedly a brilliant opening
Casual games! Unrated games.