Moreover, it explicitly breaks in VSCodium and no good alternatives exist.

Not sure what you consider "no good" alternatives. jeanp413.open-remote-ssh[0] has worked flawlessly. It's the first or second search hit in the extension manager for "ssh". It's a fork of Microsoft's previous extension before the proprietarized it.

0: https://open-vsx.org/extension/jeanp413/open-remote-ssh

You say that like it's a bad thing; I narrowly escaped serious use of VSCode thanks to this fact.

Take zed for a spin