I think they're relatively universal. Just matching the size would be the thing. Too big and your tractor is always trying to do a faceplant. Depends on the front end of the tractor too. Some aren't suited for heavy loads.If you get a tractor without a bucket how universal are the front buckets to rig up? Do you need to find an exact match or is there some sort of standard similar to the hitches?
Seems like the loaders are often made by a separate company, and they just have mounts for the different tractors out there. Or the main brands anyways.
A weight box on the back is important too, helps put the load more onto the rear axle.
Interesting thing about tractors is that they don't generally have front brakes.
So if you're going down a steep hill with no weight box and a heavy load in the loader, if the rear end gets light, it can suddenly turn into a roller skate that wants to go down the hill at maximum speed and you have no brakes.

Discovered that with mine when I was moving gravel and only had the post auger on the back. Thought I was gonna land in the pond.

After that, it's 4wd only going down the steeper hills...at least the front wheels are geared then.