Wow this has a lot going on! ✨
There was quite a handful of systems and mechanics that works, really like the vibe and setting of the game, I'd suggest to reconsider having the zombies fully immortal and probably add some sort of heal mechanic, either a healing pick up or maybe when character is low health, give a small passive healing, that way players can always have a bit of chance to low health run the game, keeps the player on edge without punishing too much.
Other than that, really solid game, if you add more polish such as SFX and ambient noise, it'll definitely elevate this game to the next level, good job!