@aral I guess I haven't seen that particular design pattern (just disabled notifications, restarted Signal, and got prompted -- "not now / enable" -- so yeah, confirming what you see. It's IMO on a par with prodding the user about their PIN, which is at worst mildly annoying but serves a useful purpose).
(I still maintain that a messaging app that supports audio and video calls, but has no notifications enabled, is effectively useless -- but end users should have the option to choose that. I'd argue a better UX here would be "yes / no / ask me later" and if you pick "no" you get an explicit warning that you will never be notified of any incoming calls or messages; at least that way unsophisticated users are aware of the risks and sophisticated ones can still make that tradeoff.
Tradeoffs are really key here, and we should support maximum end user control while also being very explicit about tradeoffs to avoid surprises.)