So we’re starting from this state in the .blend file and then exporting, right? Only image textures wired up?
I don’t see any seams when I open it if so. One very weird thing I do see is that the extensions of the images are incorrect, like Blender has mis-identified which are PNG and which are JPEG images. I wonder if that needs to be given in their names on the Image Texture nodes?
I fixed that manually, here’s the result:
ownPlanetExt-v1.glb (5.4 MB)
(reduced to 4K textures to stay under the upload limit)