It’s a good question — and really, what makes a good post will be different in different categories. Nearly all the categories are pretty tightly scoped and should be more obvious, but we do have two fairly “loose” categories: Community and Offtopic.
If you’re ever curious about the “mandate” for a given category, we try to ensure that the category description has some guidance about what sorts of topics are encouraged there. For example, check out About the Community category for the Community category. But moderators and high-trust users can move topics as needed. I’ve moved this topic into Meta Discussion — which is for discussion about this site itself.
The Offtopic category is much trickier; we don’t currently have any written guidance there. But this is still a site about the Julia language targeted for folks who work with the Julia language. I’ve long held that there are many places where folks can go to argue on the internet — we don’t need to foster that here. So we do still keep some informal limits on topics there, too, even if it’s a little fuzzier.
I think a common theme underlying the tensions in many of your topics, @Tarny_GG_Channie, is a desire to ascribe what The Julia Community thinks as though it’s a monolithic entity or what The Future of Julia should be. This elevates the stakes to a level that’s far out of proportion of what’s possible to meaningfully achieve in a forum posting. As a simple example, reframing “What should the Julia Community do to win big” to “What are you doing to ensure Julia wins big?” makes the topic far more concrete and descriptive, rather than trying to prescribe what folks should be doing.