You can still use textures though, place the texture you've made in the Textures folder similar as you would place custom objects in the Collections folder. Then you can select the texture for a material and it'll work as intended, sorry I had to cut the function for textures in custom models but there were more problems which kept it from being stable other than the bug you've reported.
Oh! – In that “Textures” folder. – I see – I confused myself because the custom cube & mats that I posted had relative paths to their own “Textures” folder, so I thought you were talking about that one before.
I hadn’t even realized there was a root “Textures” folder (next to Collections and Scripts).
And so, it sounds like, if there is a texture in that folder, then it can be applied to surfaces using global UVs? – That works for me.
It’s lame that importing objs with custom textures doesn’t work, but at least there’s a workaround. 🙂
Hey, and by the way, thanks for taking the time to explain all that to me, I appreciate it. 👍🏻