That's ok. MSFS takes multiple materials for a gLTF file.
Soooo in the end I made it to a plain single file texture.
I tried exporting like that and, WOW that
partially worked! Still I have a couple problems I hope somebody can help me with.
The only thing is that I noticed that the texture was TOTALLY wrong, and there were missing faces. You can see in the video the moment when I realized that the missing faces were due to "Backface Culling" enabled. So one issue less to ask you about.
The major problem is that in Texture paint mode the textures looks fine, but in layout view (and in the final export / ingame model) the textures are TOTALLY wrong as you can see in this video.
What can be causing it? I almost made it! It took me 3 days to make a model appear in the game environment and I am excited even tho the resul is poor and bugged!
One more step, and you can expect a full chernobyl rework soon!
Here you can see a video of the process: https://www.loom.com/share/01f14c38701e4945809fd5d9997927cf
EDIT:
The texture is fine when importing, it gets weird when assigning it to the Albedo material, as seen in the linked video
EDIT2: (28/08/2020 - 14:06GMT)
Seems like that, matching the Texture Paint window settings (Solid Mode Viewport / Texture Paint Mode) the model shows the right texturing. It fucks up when switching to Render or Material Preview mode.