Apologies for bumping an old thread. Couple of things I’ve noticed while playing around with uploading custom emoji recently:
The ‘drag and drop’ functionality seems broken (Ubuntu, Brave Browser) - it opens the image in a new tab rather than uploading. This seems to be the same for both SVG and PNG. Last time I used this functionality a few years ago (same OS, same browser) it worked correctly.
Also, the file browser that is created when you click the Choose Files button is ‘customised’ presumably so it only shows suitable file types. By default it will only show PNGs, but custom emoji also work with SVG and JPG icons too. Seems like a fairly small fix but I couldn’t work out where in the Discourse codebase that file browser customisation is made.