Hi again.
i have now migrated my notes to Joplin, and (manually) tagged them. Regarding the desktop app i have following suggestions to help improving the tagging system for the desktop app:
making tagging easier
have a line at the bottom of the window (or under the Button-bar) that shows the tags of the current note. In this case you see all tags at one glance while you edit the note.
As a bonus, when you click on a tag, it could have the same effect as clicking on the tag in the left pane - show all notes with this tag.
Middle pane (where all notes are shown): show which notes are already tagged by adding a small icon next to the title. In this case you see if there any notes that are not tagged yet.
I know that maintaining Joplin is a hell of work, so feel free to take this suggestion or drop it since there are more important things to do.
In the Joplin Android app (I don't remember if it's the same on desktop), the tagging UI currently uses two separate input fields: one for selecting existing tags and another for adding new ones.
It would be much more user-friendly if there were a single input field. As you type, it should suggest existing tags that match the input, and when no existing tag matches, an option like "Add as new tag" should appear.
This kind of functionality exists in apps like Evernote and (I think) Zotero as well.
I believe this would simplify the tagging workflow and make the UI cleaner.