What an immense tension there must be between “Trump is a fascist who would turn the US into a Nazi regime” and “all that I can or must do to stop Trump is cast a single ballot one time.”

Search your local area + the word 'mutual aid' and see if there are any groups near you. Also a good chance of meeting some at a local food not bombs event, or other volunteer work.

There's an offshoot of libertarian socialists in the DSA, but those seem pretty spread out, not sure if you'll find any locally. If you have few other options, you could try checking out a regular DSA meeting, but from what I've seen, a lot of those groups just do quarterly meetings and aren't really that active in anything meaningful, and they tend to gather more social democrats than anything. Still, better than nothing, and you may be able to make some friends there that you can invite to local direct action things that you find other people participating in.

If you can't find anything in your area, start your own! :)