Not getting notification for new emails

I have checked the following to receive email notification:
-Autostart enabled
-Sync in Android enabled
-Email frequency is set to 15mins
-Push notification enabled
-notification in android enabled
-excluded K9 from automatic app based energy saving so it is able to run in background all time.

Please help!

You left out the most important bits of information:

Which device?
Which Android version/rom?
Which version of K-9?

Hello, picture attached.
MIUI 12 on Android 10, Xiaomi Mi9Lite
latest Version in Google play, 5.806