https://github.com/LemmyNet/lemmy-ui/issues/1048
In a nutshell, many people are bringing in more or less useful comments although it has already been suggested how this could work; the changes required would touch some core functionality in the way federation is done/ links are handled, thus none of the new devs take the initiative; the two main devs are occupied with other serious stuff.

Not supported yet, last I checked (within the last two weeks). There's a feature request open on the Github.

I've mainly just been navigating to it manually by opening the community, it's usually a post near the top when I've had cause to do it. You can also use the search functionality.

Can't be done (outside of apps) without a browser extension. I can imagine a feature like that getting baked into some browsers in the future but for now you need to set it up yourself.