The horse, Llamas, and wolves don't work for me how do I fix?
I have/had the same problems as well
Except for the horse cause I don't think that I saw a horse on the world I had before Minecraft 1.21 was released. Also I didn't know that the addon affected the horse so I never thought about it while I was in creative mode to spawn one in with it's spawn egg because AntiGM didn't mention it in the comments on here as of how to interact with it after finding one. AntiGM also didn't mention the llama either and like you I've found plenty of llamas in the savanna biome.
But I bet that the llama doesn't have any interactions and animations from the addon yet.
Oh and those issues you and I have encountered are bugs that AntiGM needs to fix with an update (for minecraft 1.21 obviously), not on our end. If you installed the addon correctly that is.