For big map vehicle and infantry shooters with vehicles that run decent on the Steam Deck I recommend

Easy Red 2 https://store.steampowered.com/app/1324780/Easy_Red_2/

^ I am as tired of ww2 shooters as everybody else, but this game is just damn fun, the maps are very varied, there are lots of quality of life details but the core gameplay is actually very realistic in terms of bullet/gun/vehicle mechanics, the AI can receive basic orders and there is a small but active multiplayer scene. The planes are a blast and the variety of realistically behaving armor is great. I appreciate that you can control the cannons on tanks from the driver seat or just focus on driving and let the AI shoot (or have a friend shoot of course). Performance is superb on the deck, especially for the amount of bots you can get on screen at any time.

For some reason Easy Red 2 is 9 bucks on steam???? Like why is it so cheap? I don't know, but if you are upset at EA a great way to take out your anger is by buying this awesome game from an awesome indie dev who is the opposite of EA. Note this doesn't play like Call Of Duty WW2, it plays like a realistic-ish shooter.

Operation Harsh Doorstop https://store.steampowered.com/app/736590/Operation_Harsh_Doorstop/

^ A free moddable realistic tactical shooter on the unreal engine, it is still fairly limited and the playerbase isn't huge yet but honestly it is really promising and is already a blast if you like realistic modern warfare tactical games, gunplay and movement feels tight and locked in, weapons feel chunky and the foundation is there for a lot of great mods. Vehicles and helicopters are very early stages but are being worked on. I think this is going to be a GREAT platform for big team shooter mods of all kinds of genres and it is nice that it runs decent on the steam deck so long as you are willing to turn everything down so you are basically playing ghost recon 1 but lol... I don't really care. Check out the Star Wars mod on the workshop as an example of what kinds of different stuff can be done with modding on OHD.

Both Easy Red 2 and Operation Harsh Doorstop are great games to keep your eye on even if the specific experience of either shooter doesn't attract you right now, I could easily see a fan made spiritual successor to Battlefield 1 being made using Operation Harsh Doorstop as the basis for example so both games represent a lot more than Yet Another Boring WW2 shooter and Another Boring Modern Warfare shooter lol.

Halo Infinite also plays well on the Steam Deck, though I wish performance was better and it sometimes just crashes.

There is of course, always Xonotic available right on the linux distro app store a 30 second download away in desktop mode :P

https://xonotic.org/