I get you. I can never think of anything that would be interesting to post or ask in the more discussion-oriented communities, let alone choose a specific one to post in. I definitely find comments easier, as well as posting to more niche communities. I feel the scope is usually better defined there.
Would you say it's about not knowing if your post would be accepted in the community, or just finding the best place for it? If it's the latter, AskLemmy could be good for general questions, or failing that, any of the casual chat communities such as !chat@beehaw.org.
As long as your post meets the rules of the community/instance, I feel it's better to post somewhere than not at all - people can always crosspost it elsewhere if they like.

It's an alternative to Lemmy with some different features. Since it uses the same protocol under the hood, its instances federate with Lemmy. There's more info on the differences here.