YouTube test might not send you channel notifications even if you select ‘all’
Source: 9to5Google

Test Overview
YouTube is running a test in which viewers who are subscribed to a channel and have opted in for “All” notifications may not receive notifications if they haven’t interacted with that channel recently. “All” notifications normally alert the subscriber to every upload a channel makes.
Why YouTube Is Doing This
YouTube explains that many users opt in to “All” notifications for many channels, then later feel overwhelmed or lose interest. Instead of updating their subscription preferences, they often turn off all YouTube notifications at the app level. This can lead to missed notifications for channels that the user still wants to follow.
Viewers often opt in to receive “All” notifications from many channels. When they feel overwhelmed or are no longer interested in a specific channel, instead of updating their subscription and notifications to better reflect their preferences, they simply turn off all notifications from the YouTube app entirely. It’s common for users to have turned on All notifications for a channel, only to have turned off app‑level notifications (Creators can see how this impacts their channel in the Audience tab). – YouTube support thread
Impact on Channels
- Channels that upload infrequently will not have their notifications affected.
- Actively engaged viewers will continue to receive notifications as usual.
- Notifications will still appear in a subscriber’s inbox.
Testing Timeline
YouTube has been testing this approach for the better part of a year, initially starting in March 2025 (source).