The closest thing to Instagram that is gaining a lot of traction these days is Pixelfed - an image-based network that connects with other platforms so you’re not closed into one corporate ecosystem. Pixelfed is also working to establish itself as a non-profit, which is the gold standard for reliable tech today in my mind.
For long-format and regular updates on-topic, I think a Discourse-forum like ours is actually the best solution. You can reference it from wherever you are on the web and it pulls people into a community. I wish our forum could federate with other social networks like NodeBB does. Then you could basically blog from this forum and be connected to the world.
If you’re looking for a blog or newsletter like substack, I would recommend Ghost. They’re not part of the federated social web yet, but they’re working on it.