Recently I've had two issues:
- Mojave Universal Clipboard stopped working between Mojave and iOS 15.4.1
- Mojave notes iCloud synced but always showed a spinning activity icon
I found that I could make Universal Clipboard work again by creating or editing a note on my iPhone or on Mojave. Once that synced then UC worked until I rebooted.
If Universal Clipboard isn't working first reboot your devices and confirm connection to WiFi with Bluetooth enabled. Then try toggling Handoff off/on on both devices. Then try:
- Changing my Mojave location DNS settings from Cloudflare (18.104.22.168) to Google (22.214.171.124). (Based on this post)
- Toggling Notes iCloud off then on again (restores notes)
Now the spinning is gone, and UC seems to be working.
Update 5/15/2022: UC is back to not working unless I create a note that's synced between iOS and Mojave. Notes doesn't show the skinny activity icon. So this is an open problem.
Continuity has worked since May 2022 on my Mojave machine, but I'm now switching to a 2023 M2 Air running Monterey. And, of course, the Universal Clipboard didn't work again.
A few hours later my devices notified me that iCloud services would not be available until I reauthenticated. That tedious and annoying process requires entering the iCloud and device passwords; I think it creates a new token/password behind the scenes. After going through this continuity worked again. Signing in and out of iCloud is a common workaround for Continuity issues, I suspect it speeds up regeneration of the new token/password.
It would be nice if Apple improved this process.
PS. Typical things to check when it doesn't work: bluetooth on, devices on same WiFi, etc.