Another festival of games is live on Steam now with Steam FPS Fest 2024 running until April 22nd at 10am PT / 5pm UTC, and there's also plenty of demos for games to try too.
Shadow Warrior - 90% off (Native Linux / Deck Verified)

Black Mesa - 80% off (Native Linux / Deck Playable)

Boomerang X - 75% off (ProtonDB Gold / Deck Verified)

Severed Steel - 75% off (ProtonDB Platinum / Deck Verified)

theHunter: Call of the Wild - 70% off (ProtonDB Gold / Deck Unsupported)
Valve really need to update the Steam Deck rating, it's worked fine for a long time.

BattleBit Remastered - 50% off (ProtonDB Gold / Deck Playable)

Fallout 76 - 80% off

Fallout 4 - 75% off
Fallout 4 is getting an update on April 25th too!

Fallout: New Vegas - 75% off

Fallout 3 - 75% off