Any idea what this problem is called, blender exported glb file looking strange artifacts when closeup

[lalamax3d]

i am pretty sure, geometry is ok, (in blender) when i export n load in r3f it looks strange lines on surfaces(mesh elements/islands)
noticeable when i zoom ( go close to mesh)

when i try fbx, no issue, but materials lost..

initially i thought, might be vertices split. etc.

i tried (using gltf-transform weld command as well. still same.
i tried re-importing same file in blender (again) - without merge vertices. and they seems correct not duplicated. or split etc.

i tried disabling all normal mapping (on all shaders) still same.

[manthrax]

Super common issue with shadowmapping (shadow acne aka zfighting, and its inverse: peter panning):

OpenGL shadow peter-panning

The easy fix is to set:

light.shadow.bias = -.001 or .001

The larger cause is related to the camera near/far values, and the overall scale of your scene, and the shadow map coverage area of DirectionalLights.. (and also to some extent, the resolution of your shadowmaps)