What are you trying to do with hashtags? If it is something like view all the posts with a particular hashtag, then that is not currently supported by the PieFed API. If it is something like make a post that has a particular hashtag, then that is something that is possible to do via the API, but I am not familiar enough with the clients to say which ones support that or not.

For the former case, your best bet right now is to find the tag you want to monitor and then look at its feed. I am not really sure why tags weren’t included in the post/list endpoint, but I don’t think it will be particularly difficult to add them. I will try to take a look when I get a chance.

Fedilab, a multi-services client which speaks the LemmyAPI (Piefed claims 95% API compatibility) has what you’re looking for, including if you want them to be big buttons, small links or whatnot. Tapping a tag takes you to a more robust tag search screen etc. Available in F-Droid and GPlay.