Your universal link is missing the @instance part at the end, so it tries to redirect to a community called ‘plugins’ on the instance of whoever clicks on it.
This should work for everyone: /c/plugins@sh.itjust.works
And if it doesn’t, see the FAQ in the sidebar here; first search for https://sh.itjust.works/c/plugins on your instance so that it fetches info on the community, then you can click the above link again and it’ll work.
If you’re using the website, and if I understand you correctly, I believe the [ - ] button to the right of the comment author’s username is what you’re looking for.