There are a few ways that notifications could get blocked on the Dubb Desktop App.
Notification are shut off for ALL your apps
Notifications are shut off for the Dubb Desktop App
Focus mode is on (This applies to Mac and PC). Focus mode will block certain notifications from displaying
You blocked notifications on the Dubb Desktop App
Here are the solutions to solve these items
Make sure notifications are turned in Settings > Notifications
Make sure notifications are allowed for the Dubb Desktop app in Settings > Notifications > Applications
Make sure Focus mode is turned off
See #2