This is a serious question:  What notifications?

I've never had YouTube send me any notification as I never turned any on in YouTube settings, and Facebook (which I almost never touch, except for the account I have for my business) has never sent me one, either, at least not via my web browser.  If you're getting push notifications in the browser that's almost certainly something you've turned on (or someone else has) on the respective sites.

Also, as an aside, I stay logged out on YouTube even if logged in on other Google services.

NVDA is only reading what's being generated as far as notifications go, and you should have the option to turn those off.
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Brian - Windows 10 Pro, 64-Bit, Version 1903, Build 18362  

The color of truth is grey.

           ~ André Gide