wouldnt ever run unityex on bare metal
my point is AssetStudio is too old. the latest commit before it was archived is older than unitys engine ver that was used to build this game.
also a bit unrelated, do you have a guide how to load assets to spine from exported unity project (ik youve said previously an up to date spine ver is needed, still want to try it)
Like I said, I'm mostly using UABEA myself since it handles things better than older stuff.
As for loading assets in Spine. For .json animation files it's pretty straight-forward: you find "Import Data..." in menu and select the file you need.
And then there comes ThornSin's texture handling... so basically, game comes with standard resolution textures, like 512x512/1024x1024/2048x2048. But game's provided .atlas file contains original developer's asset information (original resolution, something like 5435x3414). So to unpack game's provided sprite sheets you'll need to do image scaling first to the resolution .atlas file provides. I'm using GIMP's scaling, but important note here: Set "Interpolation" to "None". It won't produce artifacts this way.
Once you upscaled all sprite sheets you can extract them with Spine's Texture Unpacker. ThornSin use Premultiplied Alpha in art, so you must check "Unpremultiply alpha" in Texture Unpacker. It's critical for correct image rendering in Spine.
After everything is done correctly you'll have scene properly loaded. After that... I'd suggest to learn how things work in editor.
As for rebuilding sprite sheet, this is the most painful part. You will have to pack sprite sheets to the same resolution which original .atlas file use and then rescale that image to original resolution it comes with the game. Any other resolution won't work. Sure, you can try to scale your new sprite sheet again, but in my experience it produce rough edges on sprites.
How game handles mismatch of .atlas information and actual texture resolution? I believe it's handled internally with some formula perhaps but I didn't figure it out.
So this is the method for texture handling some devs using (ThornSin is not the only one) and I hate it.