zaop

That is a pretty recent policy, from the last year or two, it’s available in a limited number of countries, and it’s a pilot you need to manually apply for. And you still need to pay the fee to Google, it’s only reduced by 4%, so instead of 30 it’s 26 / instead of 15 it’s 11.

More info: Google Play Help Center: Enrolling in the user choice billing pilot

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.

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/[email protected]

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.

/c/[email protected] is also quite active!

It’s also possible to swap out the extension registry entirely and still use Microsoft’s marketplace instead of Open VSX in VSCodium.