Can the iOS share functionality be expanded to allow file types other than txt ?
E.g. if I want to save an email I can use the "Print" function to get a pdf of that email (preview) and then share it with apps. Unfortunately I can't share with Joplin. To add it to Joplin I have to save it in a folder, switch to Joplin, then add it as an attachment, that's a lot of extra work especially if trying to do it on the fly.
This is a very legitimate concern. Some time ago, I made an iOS shortcut function for it, primarily as a Web Clipper, but you can certainly customize it for your needs. Even if it is a detour, it works quite quickly and well, and is above all individually adaptable in style and content.