Setting to disable following except for followbacks

[jonpincus]

Is your feature request related to a problem? Please describe.

Harrassers sometimes target people by making new accounts with names they know will trigger the target and then following them -- so it shows up in their notifications. For example, I saw somebody post

honestly i just wish i could wake up every day & not have a notif for “trans women are men” has followed

Even if the account gets reported and deleted as a harasser, the damage has been donw.

Describe the solution you'd like

A setting that would prevent anybody from following me unless I'm already following them.

Most people probably wouldn't turn this on, but for people who are being targeted it would be very useful

Describe alternatives you've considered

A simpler version is just to disable following completely. That's certainly better than not having any option at all, but it also lets a harasser prevent somebody from getting any new followers.

An alternate approach is just to filter out the following notifications. But people who are being harassed often want to be careful about who's following them and preimptively block likely harassers, so this isn't as good as preventing the follow.

Additional context