What is theme's base_scale? Trying to lower render resolution of my game.

Can anyone explain to me what base_scale for theme is? I tried to change it's value but it does absolutely nothing.

Currently I'm trying to reduce resolution of my simple pixel art 3D game for mobile because the FPS was so bad. But to do that I had to also downscale the UI. Before I attempted to scale all the textures and UI one by one, I thought maybe I should try to find magical solution first.

I'm also aware of resolution scaling, but it only has Billinear and FSR unfortunately, doesn't have Nearest Neighbor or no filter at all. That would ruin the pixel art style.

The game looked like this by the way.