Ukraine had always allowed foreigners to join their military to help them, only if those foreigners already had legit military training.
The Azov Brigade and the legit neo-Nazis in the Ukrainian military were always real, but it was like 1,000 people. Just like there are some violent weirdo white supremacists in the US or any other military, there are some wackos in the Ukrainian military, and much was made of their existence by other much more dangerous violent weirdos.
It sounds like the neo-Nazi interest in joining with Ukraine was similar -- it was real, but it was literally like 2 people and it's unclear if they even had the military training that would make it possible for them to do so. US intelligence wrote reports on because that's their job, not because it was anything that existed at scale.