Well I got it working. For anybody interested since recently googling "how to run ashes 2063 on fedora linux" literally gave me this thread as the first hit :sigh:
Firstly the flatpack version of GZDoom seems to be broken in multiple ways and also has issues with file permissions. Supposedly it can only read files from "~/.var/app/org.zdoom.GZDoom/.config/gzdoom" due to "privacy reasons" according to the app description. It only works through terminal anyways but just in case I put all the necessary stuff in that directory.
P.S. on my version of linux literally copy paste the above line ^ in the quotes with the ~ symbol into the address bar of your file explorer and it will take you there if you have the flatpack version of GZDoom installed.
The only 2 files you need to play ashes are a doom .WAD file and the mod .PK3 which come in separate files for episode 1, 2, 3, etc.
For the .pk3 it says in the readme "For use with GZDoom using the Doom2/FreeDoom2 iwad. No other port is supported." - I just downloaded the standalone version (even though it doesn't work on linux) just so that I could go into the resources and copy the freedoom2.wad from the resources folder in it.
I'm dumb so I figure whatever version they package with the standalone will just have to work for us right?
Anyways I copied it over here: "/home/haddy/.var/app/org.zdoom.GZDoom/.config/gzdoom/freedoom2.wad"
Then just download whatever .pk3 you want (make sure it's not just the map files but the actual full campaign) and shove it into the same directory:
"/home/haddy/.var/app/org.zdoom.GZDoom/.config/gzdoom/Ashes2063Enriched2_23.pk3"
(this is episode 1 btw it comes in a folder called "AshesEp1_2063_V2_3.zip")
Then open your terminal (doesn't have to be from a specific folder) and run the following (replacing haddy with whatever file path directory your computer has):
flatpak run org.zdoom.GZDoom -iwad /home/haddy/.var/app/org.zdoom.GZDoom/.config/gzdoom/freedoom2.wad -file /home/haddy/.var/app/org.zdoom.GZDoom/.config/gzdoom/Ashes2063Enriched2_23.pk3
The terminal should do the matrix thing for a bit and then you should be launched into the game in fullscreen. I ran around the first level a bit at time of writing and set up my display and control settings and the game seems to run like an absolute charm.
I pieced this stuff together from random reddit threads and this one website article I found while randomly googling: "
https://www.gamingonlinux.com/2018/09/a ... t-episode/" which was helpful. I have no idea where GZDoom linux terminal commands are supposed to be documented and "GZDoom help" doesn't do anything in the terminal...
I genuinely hope that this stupid thread can help someone in the future. I'm just happy to scavenge revolver bullets and rusted cans of baked beans again!