PS Find the ultima Blender Method : a nightmare for find the good process!
- merge by distance - unlimited disolve - clear custom split normal data!

Woks fine directly inside Blender for OBJ or PLY (Marching cubes) in one pass!

Thx to LOLock
https://i.imgur.com/LceY8nu.mp4

So in MagicaVoxel you make this volume in 1 second!
And can of course modify it in Moi3D (if wanted) by import an OBJ without triangulated faces!
_importOBJ by Max Smirnov