Pleroma is in a unique position where it comes to mobile / desktop applications. Because Pleroma supports both the GNU Social and Mastodon client APIs, it can work with applications for both platforms. With that said, we recommend using the Mastodon applications because they are more up to date and support most of the features of the platform.
For Android devices, we recommend Tusky. Tusky is a very good mobile app that is easy to learn.
For iOS devices, we recommend Amaroq. Like Tusky, Amaroq is a very good mobile app that is easy to learn.
Right now, there are no desktop applications that I am aware of that I would recommend. There are a few, but they use Electron, and I'm not the type of person to recommend an application written in Electron.
However, on the command line, there is tootstream and toot.