Shadow Black Lines Glitches

Together with a friend I've been working on a 3D Project lately.

However, we've encountered a weird problem we both are unable to fix:

Every single Mesh in the Scene (doesn't matter if Unity Primitive or imported from .obj files) has these black lines over it: We were able to track it down and found the reason: The shadows. However, we don't know how to fix our problem.

Increasing or decreasing / turning on/off certain settings in the quality menu doesn't really fix the issue, just make the lines more or less visible or increases/decreases the amount. Here is a screenshot from our current graphics settings. Please note that switching to ultra/increased cascades or shadow resolution only makes the lines smaller/harder to screenshot which is why I turned it off. Turning the settings to max is only the last option since our game will already be kind of resource intensive, so we don't want to make it unable to run on older PCs. Using no shadows is of course a no-go.

I've worked with Unity before and never encountered such an error. What can we do to fix that?

Thank you in advance!

P.S.: We actually want to use the Lightweight Render Pipeline, but it causes the exact same issue. If there is a fix involving the LRP which doesn't work normally we'd appreciate your help too, of course!

P.S.S.: If you need any other information feel free to ask!

P.S.S.S.: The problem also doesn't lie with the Unity default materials since our own/custom materials/shaders show the exact same problem