Edit: Whoopsie - some of this is incorrect, see Blaze's extremely helpful answer below. Many things on the Fediverse are still not intuitive, but I was mostly incorrect in stating that one of reasons is particularly wrt the dropdown menu.

Try it - you can use me + this back-and-forth as a test platform, or really at any time you can do something and click the "Preview" button to see how it will render before you send it to someone else (I do this anytime I have even the slightest encoding - it really helps to spot e.g. a backwards parenthesis that would have displayed a link rather than the link text:-). Ofc clicking it would destroy your message, so make sure to select open in a new tab, to test how it would work:-).

Basically: yes the dropdown menu appears, just as for usernames, but if you choose the item from the dropdown that you see, the Lemmy UI will do the wrong thing. My first link was made using the dropdown, while my second ignored the dropdown and just used the exclamation mark. Notice how my first link takes you to an entirely different instance? But the second link goes to the version of that community while keeping you on your same instance.

Btw, here is a post that describes all of the variations that you can try - there are more than just these two - and the relative merits of each. I highly recommend that !newtolemmy@lemmy.ca community overall btw!:-)

Oh that reminds me: there is also no possible way to share "post" or "comment" links that will auto-adjust to allow you to remain on your logged-in instance, unlike username, community (despite the dropdown route being broken), and instance links. So what you can do is on your instance click the search button / magnifying glass, then paste in a link, and that should take you right to it.

Except ofc when it does not, although with you being on a major instance there's an extremely good chance that it will... but not guaranteed. The reason is that there must be someone (else?) from your instance who has subscribed to that community first, for you to be able to see it. And that person must blaze the trail, not merely by clicking around on an existing link, but by piecing together a URL in the proper format (c/communityurlname) and then clicking subscribe, and then waiting for the list of posts to populate over the next several days. Once the first person has blazed the trail, it should work for everyone else much more smoothly, but that trailblazing process is not automated or anywhere close to streamlined. Furthermore, reasons that that might not work is that the "community url name" is not always the same as the "community long-form name" that is displayed at the top of it - those can be different. e.g. an example is "Dungeon RPGs" (a community that I just happened to see one day in the right-hand sidebar of my own instance, discuss.online, and btw it's not a terribly popular community - to this day I'm literally the only one who has ever posted to it:-D), although the url for the name is not "dungeon rpgs" or "dungeon_rpgs" or some such, but rather "drpg".

On the other hand, I mentioned that there's a good chance that it will already work - this is b/c of some seriously irl actual fucking heroes who go around making alts on every major instance, and keep very long lists of every single community that they can find, and subscribe to them. Except... not drpg, so if you attempt to visit https://lemmy.world/c/drpg you will get an error, as if that were an invalid community. It is a valid community though, it is just on a tiny instance that such people have not included in their nets - not that I'm complaining or whatever, just using this as an illustration (the top community on this instance has only 67 users per month, and its url at lemmy.world does not work either, and then the next community after that has only 18 users, and is for a small town:-D so this is a tiny instance, with virtually no actual communities).

Most of these activities, from what I can see, are done by one person, these days at least - Blaze - but like, what if they ever get sick, or lose their job, or get hit by a bus, will all such things on the Fediverse cease functioning in such a horrible scenario? I did see a post asking if people would like a bot that would do this... but even once this particular issue is solved, by a bot, it still will only be a solution for a subset of the issue. e.g. what if someone spins up a fake community, calls it "Kamala Harris rules", waits for a month and then fills it with child pornography? This sounds like a joke, but people do these kind of things, on purpose, and laugh and laugh about it. But I am not joking when I say that full-on, actual federal fucking agencies - of far more than merely one nation - will find it no laughing matter.

The whole concept of "federation" is exciting... but not terribly polished as of yet. The Lemmy UI comes the closest, having the bulk of the development efforts so far put into it, yet even here it is telling that something as foundational as choosing the dropdown menu for community links results in a URL that takes you away from your instance, when the aforementioned post explaining the URLs makes it look naively to me like a 30s change would have fixed it? (but maybe I'm missing something, if e.g. changing "example.com/c/community" to "/c/community@example.com" would indeed fix it, as it says). Notably in relation to the devs prioritization incentives: if you are a member of lemmy.ml and click a community that is also on lemmy.ml, then you are not affected. Everyone else... can wait until the developers decide to get around to it, one day. Maybe they already have even, and it simply hasn't made its way around to the rest of the Fediverse yet. But even if so, that still points to how these very foundational matters, about "whether communities show up on your instance or not", and "sharing a community link" have been broken, all this time. And again, sharing links to individual posts and comments likewise does not work - this time there is no dropdown, there just simply is no possible way for it to work (afaik, and confirmed by e.g. Blaze), without UI changes in the code.

People coming from single-instance platforms - Reddit, Facebook, X/Twitter, etc. - do not expect to see this level of complexity. This is not "intuitive" that you see a URL in your browser, yet when you try to share it to someone else, it does not work as they expect. Mind you, that is understandable - Lemmy's version is 0.19, notably very far aways from 1.0 - I am just saying that realistically, we have a ways to go for things like that to happen.