Bandai Namco Entertainment released DRAGON BALL GEKISHIN SQUADRA, a free to play MOBA set in the Dragon Ball universe and it works well on Linux / Steam Deck.
There doesn't appear to be any anti-cheat problems with this one, and no anti-cheat is actually noted on the Steam page and in my testing everything seemed to work without issues with Proton 9.0-4. It's a free to play game, and so of course - there's micro-transactions. They want you to pump some coin into it to help unlock more characters and skins for your account, so it's something to keep in mind.
As a MOBA, it does a pretty competent job at the gameplay with mixing in the Dragon Ball characters and compared with the likes of Dota 2, it's incredibly accessible and simple to get into. From the games I've played and completed, I've surprisingly really enjoyed it. The mixture of characters, the world and all the abilities do make for quite a fun and engrossing time. Especially since it works great with a gamepad, I can sit back and chill with it.
Since it's a MOBA, it's a hero battler. You pick a lane on the map, and fight through taking down specific enemies that act as the towers, while the opposing team tries to do the same to you. You'll battle various AI enemies to help your character level up, and fight other real players directly too. All in the name of trying to get to the opposite team's base, to steal their Dragon Ball and win the match.
Chaotic too at times when you're battling multiple opponents, and you're all firing off these huge abilities, you can definitely get a bit lost in it.
Performance on max settings has been without a problem, even with all the action going on with multiple characters fighting and throwing all their abilities into it - I've seen a very smooth 120FPS. Not exactly surprising though, the graphics aren't exactly pushing anything, especially as it was made for mobile too so I expected this to run well anyway. Even on lower-end machines you shouldn't have many issues with the performance in this one.
Since I was enjoying it on Desktop Linux, I checked it out on Steam Deck as well to see if it would make a good competitive multiplayer game for the Steam Deck. Especially since the controller support is perfect on Desktop, I would have thought it would make a great Steam Deck game — and it is!
Appears to be a solid 60FPS on the default settings (everything on High or Max) on Steam Deck without breaking a sweat.
Pictured - Steam Deck screenshots
From my time testing it out, this really does look like a great fit for the Steam Deck.
However, it does have a major problem.
You'll probably find that quite a few of your games can't be finished as someone quits. It's seriously abrupt too, the game just pauses with a message about it and after a few seconds that's it - game over. So if anyone has a connection problem, or rage quits - that's your game done. Very annoying.
The trailers also barely show any gameplay at all but here they are:

Direct Link

Direct Link
As a free to play MOBA, my main concern is: how long will it live? It does currently (at least on Steam) have a somewhat healthy player-base. But these types of games don't tend to last overly long on PC. At least in this case it has cross-platform play across Steam, Switch, PlayStation, iOS and Android so it might last.