Unfortunately, that's bound to go somewhere different for everyone, otherwise it would actually be a useful workaround for linking to comments. It is still kind of fun, though.
Comments and posts are using different IDs per instance so those can't be linked using a relative path. However you can use https://lemmyverse.link for those.
I'm not sure how they could fix that without having to change the entire database schema, and how to keep the posts and comments IDs in sync across the fediverse without breaking all the posts and the comments made prior to that change without processing a bunch of entries.
Well, we have a backwards-compatible solution right here. Make a database that lists how the comment and post numbers correspond (I assume that's how this works).
Storing them by hash or something would be good too, but yeah, that's a lot more work.
I'm not sure if it's different per instance, but in lemmy.world instance you go out to the feed and scroll to the bottom. You can search by user name and such.