I recently updated to a Pixel 8 Pro and my notifications are working fine. I'm using 1.6.12 of the mobile app.
Did you correctly reselect the device for your phone in the app? In the app, go to settings, Hub, reselect your hub, and then select the correct device. Then try sending a test notification from the web UI for the device.
Alternately, you can go to the same screen in the app and try to create a new device for your phone.
I too just got a Pixel 8 Pro. No issues with notifications or needing to create a new mobile device. When logging into the app, after you pick your hub just pick your old phone.