Blender import / export removes any ability to play animations on a model

Hi!
I’m in serious need of help. I have tried to sort this out for many days, but I can’t make it to the finish line.
I have this model from the asset store. I need to make an edit to the model, so I import it to Blender.
In Blender, I see there is no armature, the entire skeleton is represented only by empty points.
There is no armature, no bone weights, nothing.
Upon export, I can use the model just fine in the Unity editor, but the model shows this warning:

Sure enough, if you make a build of the game, the models are invisible, which has halted the progress of my project for a while now.

Here’s what I tried:

Using this script, I rebuilt the armiture manually. When I check it the model has weight maps and everything looks fine.
I export the model, but it seems to be incompatible with the animations. The model gets kind of animated, but it looks like a deflated blob, as if all the weights were 0.
And this is as far as I got.
Tried a million things, but just can’t get it to work. Anyone has any ideas?

Open questions:
How the hell does this model even work in the editor? As long as I don’t edit the files, the animations work just fine.
Where do my manually created weight-maps go?

I can see they got made, so why isn’t unity using them?
I would have just tried the same process to rebuild the animations, but the script I linked does not transfer animations from the points to the bones, so I’m stuck with what I got.

9689909–1382375–Slime.zip (22.8 KB)

Thanks for the reply, I appreciate it a lot!
But after two days of deepdiving into this I decided it simply isn’t worth it and just made the enemy myself from scratch.
Thankfully I had picked up all the necessary tricks since back when I got the model.