I’d suggest making sure all textures are power-of-two dimensions, no larger than 2048x2048. The skin is an 8K texture, which many mobile devices won’t be able to handle. There are errors like this in the JS console that are important:
RENDER WARNING: texture bound to texture unit 0 is not renderable. It might be non-power-of-2 or have incompatible texture filtering (maybe)?
Blender doesn’t support basis textures, no. The CLI mentioned earlier in this thread can take a glTF file exported from Blender and convert it to a glTF file containing Basis (.ktx2) textures.