As per the title.

I've already tried running it through the console to get an error reply and here is what I am getting.

start.sh: 7: Bad substitution
start.sh: 9: source: not found
start.sh: 12: get_gameinfo: not found
start.sh: 13: get_gameinfo: not found
start.sh: 14: get_gameinfo: not found
start.sh: 29: define_option: not found
start.sh: 32: standard_options: not found

I'm not tech savvy enough for this but if I'm understanding it a minimal level, this is where the errors are coming from the start.sh script. Am I reading this correctly?

Can someone help me correcting this?

Is this a fresh install of the game, or did this happen after an OS update?

Yes, those messages are coming from the "start.sh" script.

Taking a look from them I'd say your problem is that the file "gog_com.shlib" can't be found by the script.
It should be located in "${SW-INSTALL}/support/gog_com.shlib". Check if it's actually there.

Stardew doesn't like to be installed away from the home drive/folder because of poor scripting on GOG's part.

I own stardew on steam, and wanted the DRM free GOG version. So i just bought it here, and installed on POP!_OS using lutris, ran the game and.... nothing. well poo.

ok, lets take a look at a few things:
Game version: 1.6.8.24119.6732702600

(The tl;dr is, the start.sh executes the wrong file, you need ./"Stardew Valley" instead of ./"StardewValley")

I haven't looked at the two files, StardewVally vs Stardew Valley but I found that I could manually run the one with the space directly as well from,
~/Games/gog/stardew-valley/game (again, Lutris install, but where ever you installed to, will have a game directory)

So, fixing the start.sh by adding a space fixed my issue. I should look more into why its failing for the script. Maybe later.

I hope this helps!