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Do you want to see more posts about interesting topics in your Home timeline? And do you want your own posts to be noticed by others?
Here's how to do both these things:
1. Search for a hashtag you're interested in
2. On the results page, click the + or Follow button in the top right corner
3. Posts with that tag will start appearing in your Home timeline
4. Follow lots more tags
5. Include hashtags in your own posts, tag followers will then see your posts
More info at https://fedi.tips/how-do-i-follow-hashtags-on-mastodon-and-the-fediverse/
p.s. The official Mastodon Android app does not have hashtag following. If you're using Android, I would strongly advise using the third party apps Tusky or Fedilab instead, which do support hashtag following and have a lot more features besides.
Alternatively you can use the website on your phone, it works well too and gets all the latest features first.
Will the hashtag follow become available in the Mastodon app anytime soon do you think/know?
Since a huge update was just released, I'm thinking not, but I would love to have it without having to learn some other app.
Old folk don't like change.
If you switch to Tusky, I think you'll find it very easy to use. It's one of the apps that Mastodon officially recommended before they had an actual official app.
Having said that, the Mastodon roadmap does include putting hashtag following on the official Android app. It's already on the iPhone app.