Notifications
What reaches you, where, and why safety events cannot be switched off.
One event, written once, with a record of who has read it. The bell in the top bar and the Inbox on Notifications are the same inbox rendered twice.

What reaches you outside the app
The Email & Telegram tab is a grid: one row per kind of event, one toggle per channel. Link Telegram there by scanning a code and sending /start to the bot.
What cannot be switched off
Safety events - a Breach, a Lock, an Auto-flatten, a connection that needs re-authorising - are never held back by a rate limit and have no in-app switch. There is no column behind one either, which is what makes that sentence true rather than promised. The channels those events reach you through are yours to choose.
Severity
A notification's severity follows from what kind of event it is rather than from a setting, so the same thing is never urgent for one person and quiet for another.