There were several ways to search in the past weeks, it got simplified with the 0.18 update (lemmy users can check their version at the very bottom).
This means the tipps you can find from previous week and before are a bit outdated (although not completely wrong). I was confused then, and am still in the process of learning.
For now, for lemmy users, the best way (AFAIK) seems to be to search for the full community URL, like lemmy.world/c/nostupidquestions
I still think it works better when not searching for ‘Communities’, but for ‘All’, but maybe my habits aren’t updated yet.
A general technical insight about federation: New communities do not make themselves known to all federated instances. For each instance, one user has to ‘discover’ them first. This first lookup will be slower (a few seconds) and display as ‘No Result’, then switch to the result.
This means users from small instances and/or users who search for new or small communities have a chance to run into this issue.
As such, I wouldn’t trust the in-built search function too much, but use external tools to see what is out there. Once you know a community exists, you know when to ignore the ‘No Results’ message and wait longer, or ask for help.
Once you are the first subscriber from your instance to a remote community, you also don’t get the full history of posts and comments right away, but something like 20 only. So your logged in view (relative, such as /c/nostupidquestions) may show much less content than the native view (first link, full community URL).
One more thing to understand: The development is active and ongoing. Not only did many users join, but also some developers.
PS: We should use the wiki much more for these things. This would also allow the answers (if they link to the wiki) to remain updated, instead of outdated answers in older comments.