cybereality I just tried enabling Import S3TC BPTC under VRAM Compression (Import ETC2 ASTC was already enabled), but no dice. I don't see anything about lossy compression - did you mean lossless? In either case, that didn't work, either.
I'm thinking the cause of the issue is that I moved the resource files shortly before updating to Godot 4.1. I just checked the debug when running the Windows export, and it's showing exactly the resource that it's failing to find. It's definitely the PNG texture that's not being found (and I find it really weird that the engine's finding it just fine in the editor and while testing, but not when exporting).

I've also occasionally been seeing "invalid UID" warnings when starting the editor.
At this point, I'm thinking my only real recourse is to just scrap the current implementation, reimport the character model and texture (in the correct place this time), and rebuild her again. I kind of want to make a small tweak to the model anyway, so this is an opportunity to do that.