You can make it show up by clicking on the gear icon next to the search bar and ticking the checkbox next to the Allow Incompatible Skeletons option (which is on the very bottom)
However, your animation asset will show up as blank when you do so. So what’s going on in your case is that you either didn’t properly import the animation assets, or you’re trying to use an animation on an incompatible skeleton.
Hope this helps! 