Thanks ascents! Since other Godot games run well,I'm not sure if it's the fact that it is Linux. My guess would be the shader and/or the amount of shadow-casting objects. (and the lack of a decent graphics card on my end xD)
Hey, I just played through the whole game, It's some sort of issue on the games side. My graphics card (an RX 6750XT, roughly as good as a 3070) was not doing so well (it was at ~90% usage), although the game ran well for me, if you were curious. (Sorry, dev!)