To answer the question in terms of things you personally can do, I think the boring and realistic answer is to research organizations who align with your goals and who you think have effective methods, and get involved with them.
Personally I like represent.us - They’re specific to the US, but their idea is to put anti-corruption laws into place that help remove the influence of money on the government. This would help get laws passed that favor everybody instead of just the rich. Their approach is to begin at the local level and get enough momentum for a national movement to have some power.
Here are a couple of videos they made, first about what the problem is, and second about how they are trying to solve it:
Make sure you go to Settings and select any languages you want to see as well as Undetermined - I had a similar issue which was fixed by doing this.
If that’s not it, it may be a delay in comments federating if it’s a community you just recently subscribed to, or there could be federation issues. If the post is on an instance that’s defederated with yours, I don’t think it would show up at all, unless the defederation happened after it was made.
You can check who an instance has defederated with by checking the Instances link at the bottom of the mane page (or adding /instances after the URL). There’s also a tool to see what other instances have defederated with a particular one here: defed.xyz