There is no good way really.
Lemmy's search is pretty lackluster. You will have a hard time finding what you are looking for, unless you are searching for something verbatim, and if your query contains common words...Good luck. It also has no search operators.

When it comes to search engines, only google is somewhat usable (from my experience), but it's very much hit or miss. Sometimes you will be able to find the post, just by typing lemmy [post title or part of it], but it will almost never be in the top results.
And most of the time , first result is Reddit...

You can try using https://fedi-search.com

It basically just uses this query for "more accurate search" [search query] (intext:"modlog" & "instances" & "docs" & "code" & "join-lemmy")

And this one for normal search [search query] (site:lemmy.world OR site:lemmy.ml OR site:lemm.ee OR site:hexbear.net OR site:sh.itjust.works OR site:lemmy.dbzer0.com OR site:feddit.de OR site:kbin.social OR site:mastodon.social OR site:mastodon.cloud OR site:mstdn.social OR site:mastodon.online OR site:mastodon.world OR site:libre.video OR site:video.antopie.org)

Which is not just for lemmy, as you can see

Here is the search query I made for the top 35 lemmy instances (by active users) based on this: https://lemmy.fediverse.observer/list

[your search query] (site:lemmy.world OR site:lemm.ee OR site:sh.itjust.works OR site:lemmy.ml OR site:hexbear.net OR site:lemmy.ca OR  site:programming.dev OR site:lemmy.dbzer0.com OR site:feddit.org OR site:lemmy.blahaj.zone OR site:discuss.tchncs.de OR site:lemmygrad.ml OR site:sopuli.xyz OR site:lemmy.sdf.org OR site:lemmy.zip OR site:beehaw.org OR site:infosec.pub OR site:aussie.zone OR site:feddit.nl OR site:midwest.social OR site:feddit.uk OR site:slrpnk.net OR site:reddthat.com OR site:lemmy.one OR site:jlai.lu OR site:pawb.social OR site:lemmy.kya.moe OR site:lemmy.today OR site:startrek.website OR site:feddit.it OR site:mander.xyz OR site:ttrpg.network OR site:lemmings.world OR site:ani.social OR site:feddit.org)

In SearXNG u can use !lepo to search lemmy posts but it's basically just lemmy's search.

I use the Voyager app on Android and the search function is great.

There doesn’t currently seem to be a direct way to go about those search methods, as far as I’m aware.

The closest equivalent I know of to search by title:

• Go to the search page of the instance of your choosing (ex. https://lemmy.world/search, or https://lemm.ee/search). Larger instances will tend to be more useful for this since they are more likely to be aware of posts from any arbitrary instance; if you know that you want to search within a particular community, then searching on that community’s instance would yield all possible results, which could potentially not happen with a non-local instance search.

• Filter to search only posts. This will yield both posts with the term in the title as well as posts with the search term in their body text.

• Use your in-browser Find tool (ctrl+F for Windows, or Command+F for iOS desktop, or other methods with other OSs/devices) to search for the same search term on each page of results to highlight only the posts which have the term in their title.

There is not currently a flair system set in place for Lemmy. One workaround is adding the intended flair to the post title and following the aforementioned method for title search. This only works on posts for which the author has the flair in their post title, which typically is done with parenthesis or brackets before the title proper. I’ve attempted to implement/futureproof this on the lego@lemmy.world community for posts that I would want flaired as [MOC].

These filters that you’ve mentioned, as well as others, would be very useful to see on the fediverse in the future.

laughs in complicated steps

Kagi's "Fediverse Forums" lens.

I use Kagi's "Fediverse Search" lens and I've found it to work quite well for finding posts that I sort of remember and want to find again