As you see there are lots of planes, this is grass, which was a Particle System before but I decided to convert it to mesh in order to export it (before converting it was not exporting). Now, after converting the grass to mesh, I see that the grass material is not present in the GLTF viewer model.
This is how the textures should be:
And this is how it looks in the browser:
The white cube in the middle is a cube that I made to see what was the problem; I assigned to it the same material that the grass and it doesn't show up either in the browser with three.js
Blend file link: