Apple Calendar on my Mac and iPad does not sync with Calendar on my iPhone and Apple Watch. Same Apple ID across devices. Desktop Mac is Mac mini (M2 Pro): Device was not available to choose under "Devices" below.
Mac mini (M1, 2020)
Make sure Calendar iCloud is turned on on the iPhone in Settings > [your name] > iCloud > Show All. If it is, turn it off, restart the iPhone and turn it on again.
Thanks. After your suggestion, I tried that a couple of days ago. iCloud was on. Turned off, restarted, and turned back on. Waiting to see over time if it works.
Why is Calendar not syncing across devices?
