YouTube tests smart notifications for channels you subscribed to
However, if you really like the YouTube channel, you can set notifications to "All" so you always receive a notification on your phone when a new video is posted, for example.
The problem here is that over time, the channel may become less attractive, and therefore, when you do receive its notifications, they are ignored.
What users usually do in these cases is disable YouTube notifications completely, and Google doesn't want this to happen because it will lose users altogether.
A new system has been spotted in YouTube beta that reduces notifications from subscribed channels you no longer visit frequently.
This means that if you're already subscribed to a channel and set it to receive "all" notifications but you rarely visit it anymore, the app will reduce the number of notifications.
Once you log in again, you will receive a number of notifications from this channel as before.
This will prevent users from completely disabling notifications from the app, making it easier for users to feel overwhelmed by having to do it themselves across all the channels they subscribe to.
It remains to be seen whether this smart notification management will eventually make it to the stable version for all users or whether it will simply remain one of the many experiments being tested.