Request: a one-time informed consent to reply-notifications

As in GDPR but valuable otherwise, I’d like a way to show new users an opt-in checkbox right when they first post something. The state they choose then will be set for whether they get notifications of replies in general.

I could imagine other ways to break up the settings for replies vs PMs vs @mentions and even per-post settings, but the core point is just to prompt at least one time an informed-consent.

If this is somehow already possible, I’d like to know. Thanks