Logitech Circle Doorbell stop sending notification (doorbell button) after iOS update to 14.5.1

I have the exact same issue, however if i enable all notifications at any time ( Time any with activity Notifications ) then it works so you could try that as workaround

Only problem is the large amount of movement detection messages you also recieve.

I have found no app in apstore specificly for this door bell @rose_10

Hello MrXYZz,

Welcome to Apple Support Communities. We're happy to help with this trouble you're having with the doorbell notifications. After updating the iOS you want to make sure that your devices, as well as the app for the doorbell are all up-to-date. Follow the guidance as needed:

Update your Apple Watch

How to update the software on your Mac

How to manually update apps on your Apple device

Let us know if this helps you. 

Problem SOLVED. I removed the device from My Home. Then re-connected it back to My Home as a new device. AND SOLVED: notifications started working on all devices.

Doorbell notifications not appearing on iOS device…

Installed Logitech Doorbell, appears to be functioning, shows up on HomeKit & Apple TV when I press bell, as camera well visible when I access via iPhone. Problem: bell does not set off notification on iOS device… I have followed all the instructions: all devices updated, on the same network, same user ID, iCloud on, Keychain on, notifications set to Notify via HomeKit on and turned on via iOS device.

I turned it all off and back on again and still no notification for motion sensor or bell trigger from the doorbell camera… please help! Thanks