However, in the #Fediverse, hashtags are the best way to be discovered by people who are (1) not following you; and (2) not watching their “Federated timeline” feed.
While group tags (like chirp.social and a.gup.pe groups) is more of a filtered discovery tool, wherein only those following the group will see your posts.
However, if the other users are using the custom frontend phanpy.social then they can see the “Local timeline” of pebble.social. Or, if the other users are using #Firefish or #Qoto and have set it up to monitor #Pebble's “Local timeline” then they'll see your posts regardless.
But most people are using the mainline Mastodon software, which lacks the feature to see “Local timelines” of other instances; so #Pebblers on other instances won't see your content unless someone they are already following re-shared / boosted your post.
Here's a screenshot of how I set up my #Phanpy (https://phanpy.social) for my #CIM (https://c.im) account. There are three layouts available, I'm using the multi-column layout.