@RolloTreadway

I'm using the Mastodon Android app.
No way to follow the hashtag #Birds appears when I click on #Birds.

The option appears when I first use a web browser to browse to my instance (mastodon.social) and then log in.
And then click on #Birds. Over in the righthand column is #.
I click that and then go to the righthand side of the line with #Birds and find the grayed-out "head and shoulders" icon with the + sign.
Clicking that brightens it and adds #Birds to my followed hashtags.