A quick forum search would have led you to the answer. This has be asked so many times there is an entry in the FAQ near the end:
Notification appearance settings - Android 8.0 and newer
I didn't learn anything new from the FAQ. I did allow notifications in the phone settings. See screen capture.
Besides, it always worked with Android 8 and 9, but suddenly stopped working a couple of months ago. I even reloaded settings from a backup taken when notifications were working.