To stop sharing messages from iPhone to Mac, follow these steps:
1. Open the Messages app on your Mac.
2. Click on the "Messages" tab in the menu bar at the top of the screen.
3. Select "Preferences" from the drop-down menu.
4. In the Preferences window, click on the "Accounts" tab.
5. Select your Apple ID from the list of accounts on the left side of the window.
6. Uncheck the box next to "Enable this account" to disable iMessage syncing between your iPhone and Mac.
7. Close the Preferences window.
By following these steps, you will stop sharing messages between your iPhone and Mac. This way, you can keep your messages separate and avoid any unwanted syncing.