Shadows appear inside angles, this effect is even more visible when activating POM.

what resource pack is that? also the dark spots on the edges is ambient occlusion

its not ambient occlusion, but the actual shadowmap.
this is a side-effect of trying to workaround another issue with the shadows, and is a minor artifact usually. shadows can get kinda funky on spots with deeper POM, and make it alot more visible.

what resource pack is that? also the dark spots on the edges is ambient occlusion

Pixilli; in the screenshot I was using Pixilli V29, (I edited it to remove the spruce leaves textures because they looked ugly).
Now I updated to the last version you can find here (spruce leaves still look ass):
https://modrinth.com/resourcepack/pixlli/versions#all-versions