(tldr, open source software has come a long way, and it's more than possible to create a full game without leaving Linux.)
So I've been a full Linux user for a couple years now, and a hobbyist game dev for way longer. I've always tried to make the most out of free tools, so I've used a lot of FOSS tools for game development before.
Going with that philosophy, Year Unknown's development has cost $0 (not counting store fees or my time), and the development is done with almost entirely FOSS software like Godot, Blender, GIMP, and Audacity. The only exception is Reaper, which is my DAW of choice (but to be fair, it's a really good DAW).
The game itself is a narrative-driven exploration game set in the very far future, where humanity has found a way to make the universe last forever. The game's story covers a lot of existential issues that come from the premise, revealed through two characters you can talk to through terminals.
I know there's other developers who have done the same, but I thought I'd share my experience, and I can answer questions about the workflow if you're curious, or trying to do something similar. Also, if the game seems interesting to you, a wishlist would be very appreciated!