yup, the AfD is full of literal nazis. voting for them is probably the worst you can do. but some people see it as a form of protest, so as long as the other parties are shit as well, they will accumulate more votes.
Die PARTEI has several big problems as well: There have been several allegiations of sexual abuse by high ranking members of the party and their leader signed a petition to stop the delivery of weapons to Ukraine among other questionable things.
I would recommend the Tierschutzpartei if you want to vote in protest.