I (intentionally) removed the Calendar plugin from my vault on desktop. When I synced my vault to my iPhone, the Calendar icon that had been in my left sidebar at the top (along with Files, Search, and Bookmarks) is still there, but I don’t see a way to remove it. It’s pretty annoying having that there.
If you click on it, does it show anything? “Plugin no longer active” or something like that? If so, there should be some buttons with a “close” at the bottom. Maybe? Hoping?