I was just wondering, can opinion based questions be posted on the meta? Or is it discouraged here like it is in regular world building?
Some meta questions are inherently opinion-based. Yes the close reason is available, but the same base set is present on every site, main and meta, on the network, so I wouldn't read too much into that.
Questions about our scope, about what our policy should be on some point, or for that matter about what to name our robot will evoke opinions. That doesn't make them wrong. Answers should still support those opinions in some way; just saying "unicorns should be off-topic" doesn't help anybody. And questions still need to be about the site (or the SE platform in general); don't use meta to ask people what their favorite movie-worlds are.
See what is meta? in the Help Center for more about the purpose and use of meta.
Questions about the Worldbuilding main site that are primarily opinion based are not on-topic here on Meta. We still have an option to close questions here as "primarily opinion based". Though I think we're far more lenient here.
If you mean Worldbuilding questions (but would be off-topic on the main site) that are not about the Worldbuilding main site, the answer is still no. Those would both be off-topic and primarily opinion based.