Yikes :| Yeah so luckily I've never come across those...

If you've ever seen someone chanting "From the river to the sea", that's a euphemism for "kill all the Jews"

No it is not. In the mainstream, is either that Palestinians should have full access to their historical lands, or at its extreme that it should be a fully Palestinian state. Of course some people on the fringes take it further. From the now hard-right Israeli side, Likud literally used this expression in its initial charter[1], and N. dog whistled it in recent statements about two states.

1. https://www.jewishvirtuallibrary.org/original-party-platform...

That's very far, etnically and ideologically, from "Stomfront nazis" though.

In my experience, these kind of extremists kinda get banned immediately. I might be wrong though: do you have any example of right-wing accounts publicly saying that one entire ethnic group should be killed?

There a fediverse instances that are explicit homes for such content. I don’t read them. They are blocked from most mainstream servers.

Apologies, I thought you were talking of X / Twitter.