I've done something really fast, I don't know if it's the export you need, but hope it helps, maybe you can tell me what type of export is needed.
see post here : https://csmndev.itch.io/simple-polygon/devlog/863809/added-gms-14-d3d-code-expor...
Hi Cosmin,
I created a six-sided cube with 24 triangles.
I have pasted a pastebin link below, of what the example export looks like. I believe the very first line means the version number which can be left as is.
In GameMaker 1.4.9999, I can load the D3D model using this script. For example: cube.d3d
A cube In D3D GameMaker format
https://pastebin.pl/view/4740a2a1
Script
https://pastebin.pl/view/7e678b29
Let me know if you need anything else. Thank you for doing this and take your time :)