[pimlottc]

Next time you get a notification from a sender you want to silence, swipe left on the notification, then tap “manage notifications”. That should take you straight to the notification settings for the specific app.

[Nextgrid]

That still doesn't address the problem - on iOS, notifications are "all or nothing" for any given app.

[pimlottc]

Yes, unfortunately there is only so much you can do.