Did you install the official Reddit app? Same happened to me when I did. They seem to enable notifications for recommended posts once you log in. I turned that shit off and deleted the app. I don’t want any settings changed by the mere act of logging in somewhere.
I used the official app on my phone and I had turned all notifications off. I left for good before the black out and never looked back. Then miraculously a week after the blackout the app turned on notifications and started spamming my phone. I deleted that shit immediately.
Which is exactly what Twitter did. Even with all notifications off, I still received several daily tweets about what Elon had tweeted. So I uninstalled it. Thankfully the PWA isn't quite as bad, but it still pesters me with tweets that it knows I'm more likely to engage with, because they are negative.