Apple could do users a service by simply implementing a whitelist, or alternate call handling feature in iOS.
iOS can already accept calls only from a user's contacts, except that it's restricted to Do Not Disturb mode. Free it from that constraint, make the behavior available all the time and it could solve a lot of problems for many, if not most users.
Complement that with the option on how to handle call not in contacts, or without caller ID -- a specific ringtone, highlighted notification, or automatic rejection. Hell, even old POTS landlines have had the last feature for years.
It would be simple to configure (without having to dive into specific ringtone assignments), allow DND to be used as intended, and avoid false positive missed incoming notification from always-on DND. Those who need to regularly accept calls from unknown numbers can simply not enable the options.
No apps, contact exposure to third parties, or other subscriptions needed for those who only want basic protection.
Given the state of things, a whitelist, rather than blacklist, approach seems warranted.