If anyone is still having issues, this works for me:
You have to click on the Tags header at the top of all your tags. A list of tags will then come up to the right and then, you can click on the ellipses (the three dots) by your tag, which finally allows you to delete it.
This is cumbersome and unintuitive. It should happen in the main sidebar, but it works for now.
This doesn't work if the tag was in a shared note. Then, you only have the option to add to shortcuts.
Permanently Delete Tag
in Organization
Posted
This doesn't work if the tag was in a shared note. Then, you only have the option to add to shortcuts.