Is there a foolproof legitimate way to browse or search a list of communities on another instance without going to that instance or using a third party site?

That's currently a pain point for lemmy in general. AFAIK, that's the standard way for community discovery at present.

I maintain a Lemmy UI called Tesseract, and I've built in a community browser that eliminates most of those steps. You still have to know what instance hosts the community you want, but it's as simple as typing the instance, clicking into the community, and subscribing. You can also search/browse the communities of any Lemmy instance you interact with.

It's on my roadmap to use the data exports from Lemmy Explorer and integrate that into the UI itself. Then finding/subscribing can be a 1-click affair.

What app are you using? If you’re on iOS, I know the Voyager app allows for selection of filtering your search to Communities, Users, Posts, etc. and Lemma has a pretty good smart search that has found the communities I was looking for.

As far as I am aware, at least one user on your instance needs to be subscribed to a community on a different instance or at least specially searched for it to be searchable. In your case, if no one on lemmy.world is subscribed to or specifically searched for lemmy.radio/c/amateur_radio, you wouldn’t see it on a search from you lemmy.world account. Otherwise you’ll need to use a browser to find the community and seek it out on the web. Not super streamlined yet, I agree.

The only other more functional browser searches that I know of are:

https://lemmyverse.net/ and https://browse.feddit.de/

a) you don't

b) again, you don't

In order for off-instance content to appear in search (or at all) it has to have been federated, and only communities that have at least one subscriber from your instance, are federated. If some other community on another instance has no subscribers on your instance, it doesn't even appear in "All". To get that first sub, someone just has to "know" and write its exact name in search, for your instance to reach out and establish federation of the off-instance community. Most apps can't even do that step, you have to do it via the webUI, though I know Thunder can do it since a recent update.

The reason an instance can't search the entire fediverse, is that it doesn't know about the entire fediverse.

External web pages like lemmyverse.net don't either, but unlike instances they go out looking for what's out there, rather than only connecting to communities at least one user has told it about like the instances do.

The idea is to only cause federation traffic between instances where its actually wanted. For a truly fediverse-wide search, every time you search, your instance would also have to ask every other instance for search results, then return and compile those thousands of results from thousands of instances. It's not a sane way to do things.

In the future, it's more likely that instances or clients will connect to "search providers" like lemmyverse that maintain indexed databases of the fediverse, and be able to get results without hitting the actual network with a search query at all. It's possible some form of more advanced indexing will become a part of the instance server software itself.

But vry little work around this has been done, but you can see it in places. Thunder, the client I've worked on, only has basic search right now, but there has been talk about solving this problem within the app, eventually, by providing results from lemmyverse.