The horseshoe theory 100 % applies to Germany and most certainly to other pluralistic countries too because the far left and far right are fishing in the same pond, for socioeconomically weak voters. They thus end up also sharing some views that you wouldn't expect to resonate on both sides like reducing immigration.

The people who desperately dispute the horseshoe theory are usually politically extreme themselves and hate the thought of having such similarities with the opposite end.

fyi good article on where the ends of the horsehoe have bent toward each other I think: https://www.bbc.com/news/world-55957298