ok. for one, read the wikipedia page but i suggest reading one that was edited before he died just because after he died there's been a lot of changes
https://en.wikipedia.org/w/index.php?title=Alexei_Navalny&oldid=1189517416#2011_parliamentary_election_and_protests
some bits to back up what i said
He was behind the 2006 Russian Nationalist march
In late 2006, Navalny appealed to the Moscow City Hall, asking it to grant permission to conduct the nationalist 2006 Russian march.
This was essentially a giant protest against immigrants. There were many neo-nazis including people holding swastikas. if you look around long enough, you'll find a find of navalny there with some swastikas behind him. i can't find the video right now but i found some images of the russian march which should be enough to show there were neo-nazis there
please see following images i've placed into an imgur album: https://imgur.com/a/m5JQxIH
he founded this organization: https://en.wikipedia.org/wiki/National_Russian_Liberation_Movement
National Russian Liberation Movement, which made anti-immigrant its main policy. During this period of time he would make certain statements like
"muslims are cockroaches that need to be exterminated" "immigrants are like cavities, you need to pull them out" etc
"Everything in our way should be carefully but decisively removed through deportation," Navalny said in a video dressed as a dentist, comparing immigrants to dental cavities.
here's an article that goes more in depth: https://jacobin.com/2021/01/alexei-navalny-russia-protests-putin
while it's true that the Russian regime has illegally restrained him - they arrested him, tried to poison him, and ultimately killed him - but he was still a neonazi