This locked thread refers: https://www.techrepublic.com/forums/discussions/error-on-instagram/
The popup is:
“Your request is pending
Some accounts prefer to manually review followers even
when they’re public. Let us know if you think we made a mistake.”
The above is a lie. No public accounts (versus private) prefer to manually approve followers. In fact, there is no such user option. If true, then the account would be private.
This issue only occasionally occurred in the summer, now it seems to be the norm for many users. I’m only posting for reference purposes.