I mostly screw off on lemmy while I’m supposed to be working, so I exclusively use the desktop interface in a browser. From what I understand, the different apps and interfaces don’t all quite support displaying the same types of content or even markdown… yet. For instance, a I had another poster tell me that spoiler tags don’t work in the Boost app.
I think you can upload just about any damn fool thing as an inline image and the server will take it; it’s just a matter of the client being able to make heads or tails of what it is and display it appropriately.