Before getting into my feedback, I noticed the full soundtrack goes over 30 minutes, which was the maximum runtime that was set before the beginning of the jam (I know I said I'd offer a bit of wiggle room in a comment elsewhere). Also, audio files were requested to also be uploaded to your itch page as well. I'm not going to disqualify/remove this submission, but I want you to be aware of this and I'm going to be more strict about these things in the next jam.
With that out of the way, here's my feedback:
Main Theme - Very atmospheric, and an interesting take on a main theme. The mix of what sounds like breathing and the beeps of a machine is actually quite thought provoking. Feels almost horror-esque.
The Beginning - Quite dark all around. Good choice of harmony, and I like that you went with what sounds like an organ for this track. Especially considering the context.
Betrayal by Balkor - Little bit of clipping at ~0:54 (hopefully just on my end). Somewhat short overall, I think the melody you had in that lower register could be developed a little more so that it was a more structured element of the piece outside of the ambience and textural components.
Balkor, the Mad Inventor - I like the percussion in the beginning, for some reason those kinds of sounds/textures feel like 'madness' to me. The change between the phases of this boss fight are quite different but still manage to maintain that madness element IMO. I think the pad at ~0:40 is a little muddy to my ears and takes away from some of the clarity of the mix overall, again IMO.
Abandoned Village - While I like the vibe overall, I think the reverb gets a little muddy and makes everything a little hard to hear. I've found that putting a high-pass filter after my reverb plugins has helped with this a bit.
Breaching the Corrupted Temple - My notes and feedback for this track are similar to those of the last. I think you do a good job with some of the harmony, but the mix overall sounds a bit muddy to my ears.
Tarcon, the Corrupted One - I'm getting a bit of clipping on my end starting at ~1:20, not sure if intentional or not.
Battle Against Corruption - The percussive elements in this track are quite good, and I like some of the sound design you used as well. I think there could've been a little more of a melodic presense IMO, especially for the first couple of phases. Also would've really liked to have heard a little more development with that lower choir at ~4:10, I think that could've been an interesting sound to explore for a boss phase.
Give the Beast a Chance - Quite a haunting atmosphere throughout, like what we hear when we boot up the game. Really glad this returned, as it's especially fitting for an ending I think.
Back Home - To my ears this has a similar vibe to the last track, whereas the description makes me think this should be a touch brighter. Still a neat track, but maybe not quite as fitting as it could be, especially that first ~2:30.
The End - This feels like more of a proper ending to my ears. There's still those darker undertones, but the melody still feels uplifting in a sense.
Overall this was a solid and well thought-out submission. Clearly a lot of work went into the lore and world-building. It deviates a little bit from the theme for my taste, but executes its ideas quite nicely. IMO the overall mix and lack of some melodic presence in a few of these tracks are what's holding this back from being 5/5 across the board. I think if these elements are addressed then this will be an even better soundtrack that's deserving of a game being.
Thanks for sharing what you've made, and keep up the good work :)