I was also facing the same issue until today.
Anyone who's facing Delayed or No notification issue, or getting notifications only after opening the particular apps, here's the solution.
Best of Luck! 🤞🏻👍🏻
Same for me. Adaptive Notifications is definitly off, and I've been through all 1000 other suggested settings. There is nothing left to turn off and I'm still getting no or delayed notifications.