This game is 100% off until July 1st:
>https://store.steampowered.com/app/624690/NEXT_JUMP_Shmup_Tactics/
I don't know if it's good, and I don't really have time to play it tonight because I have to go to bed, but it looks like a turn-based shmup — and the Linux version Works On My Machine™ despite the majority of Linux gamers always swearing that native games are invariably broken two years after release (whereas this one hasn't been updated in nearly 5 years according to the depot timestamps found on SteamDB). Must be that Steam Linux Runtime magic.