Thanks for the clarification. I had misunderstood you. Actually, you've just introduced me to a new feature I didn't know about!
I just tested turning off notifications for a contact I use for 2fa and then tried signing in to that account.
And for me it worked. I received no notification at all for the new SMS message from that contact and had to open the app to view the message.
I don't know why this is not working for you. Hopefully somebody else who has a better idea will see this and offer a suggestion.