First of all, thanks for the Linux port, I was one of the people asking for it in stream chat.
This looks like a very ambitious project. On one hand, what you have is really impressive already, and on the other, there's a lot of janky stuff that needs to be ironed out. The AI definitely needs more work, right now it's hard to figure out what it's even doing and how it's gonna react. Also, the 3rd person camera is unwieldy and can go through walls at times.
On the good side, I really like the mobility you have with ledge grabbing here, and the stealth has potential with shooting out lights and using the nightvision to gain an advantage. The light bar in the HUD is a nice idea as well.
Not sure if there's any sort of ending in this demo, I got to the cathedral and tried exploring around but didn't find much.
Finally, some issues I had with the game, and short clips showing them off:
The mouse cursor isn't locked in place even when it's hidden during normal gameplay, making interaction really difficult, you pretty much have to open the inventory to be able to pick up items. I think this is a Linux version bug only since I haven't seen anyone else mention it. https://files.catbox.moe/2vaan9.webm
After dropping a gun with ammo still in it, you can still fire it until you equip something else. (Might be a fun way to ambush enemies though, you could polish it up to be a proper feature.) https://files.catbox.moe/b02wcw.webm
The performance varies a lot depending on the direction you're looking. Guessing by the huge changes in the draw call count, you're probably rendering a lot more than needed at all times. Although this wasn't really a problem on my system, it might become one with larger and more complex levels. https://files.catbox.moe/e8g14f.webm