Welcome!
One tip is that most of us “use” Lemmy a bit differently than Reddit. Most niche communities (with some exceptions ofc:-) here aren’t as active as they were on Reddit, so many of us end up spending more time in the generalized ones - e.g. !technology@lemmy.world rather than specific ones like r/OnePlus or even r/Android.
Another is that Lemmy requires more “curation” than Reddit’s r/all or r/popular did. If you subscribe to the communities you want then your Subscribed feed should have good stuff, but that requires your attention first, and many of us just surf the All feed to make sure we don’t miss things, and then block communities that we will never ever want (sports, highly specific locations, foreign-language ones that did not set their language preference, etc. - all of these can be viewed while logged out but then when you log in they won’t fill your All feed).
Another aspect of curation is that this place is fairly diverse & varied - think like r/conservative and r/liberal. So you may want to block some Fediverse “instances” that your own instance has not yet, to maintain your own sanity - you would do this in your Settings, Blocks, scroll down to Blocked Instances and add the name there. With you being on Lemmy.World, the main one lemmygrad.ml is already pre-blocked for you, but you may consider others that you want to add. Hexbear.net is another extremely common choice, if you don’t like that style - hint: the word “consent” seems to mean little to them, and my experience on the Fediverse improved 95% after blocking them. Sadly I recently blocked Kbin.Social too, despite that being my first Fediverse instance, b/c the owner has been MIA for so very long and also refuses to share administration duties with anyone, so all of the spam that I was seeing on the Fediverse was spreading from defunct communities there that mods had abandoned and the admin did nothing about. And just to be comprehensive, the other instance that many people block is, ironically given that it is where this post is, Lemmy.ml. I am not advocating for that one, and I don’t block it myself, just saying that many people do - and I get it, b/c 80% of the time when I get the most batshit insane replies, it is from that instance; though there is good stuff there as well… sometimes:-P, and it is just a large instance so it is going to have a lot of bad as well as good actors on it as a result.
For myself, I am enjoying Lemmy way better than I ever did Reddit - this is perhaps what Reddit used to be, before I visited it, and before it killed itself. I hope you find ways to enjoy Lemmy for yourself too!:-)
That would triple the number of mods required, for one, and with complicated cross-reporting like “spam” would get removed from all but “lack of relevance to community” may only be removed from some.
Perhaps an app or base Lemmy itself could implement a keyword system to selectively highlight all posts from multiple technology communities that match the word “OnePlus” and deliver them to one place for consumption.
But either of these solutions would require effort to build.