Apples Focus mode is useful if not overcomplicated feature which I use frequently. I find it useful when I am working to set do not disturb on my Mac so that I can respond to messages and notifications when I feel it’s appropriate. And at night so that annoying email messages are not coming through on my phone. Unfortunately, “Share Across Devices” located in Settings > Focus is enabled by default, which has meant numerous missed calls on my phone (our doorbell rings my phone so that I can speak to whoever is at the door, usually a courier).
To stop this syncing
Open the Settings app
Just above Screen Time, tap Focus
“Share Across Devices” — tap the toggle to turn it off