Unusual popups

If running iOS 13 or earlier versions, check: Settings - Passwords & Accounts - Accounts - Any rogue entries here? If so, delete the rogue account. 

If running iOS 14, check: Settings - Calendar - Accounts - Any rogue entries here? If so, delete the rogue account. 

joeanna72 wrote:

What’s a rogue account?

One that you knowingly did not add. Such are added when a user accepts an offer from a web site to “Send Notifications” or such.

You are welcome.