MacOS Ventura Calendar - After editing an event, focus jumps to a different day

Hello Pierre,

If the Calendar app is behaving unexpectedly after editing events, let's first ensure that your client is following the steps in the 'Modify an event' section here to start to isolate what's happening: Add, modify, or delete events in Calendar on Mac

If these are the actions they are performing and this behavior continues, then we would recommend they update to the latest version of macOS, 13.1. This installs feature improvements and bug fixes that can resolve issues like this. These steps from Update macOS on Mac walk you through how to back up and update the Mac:

Before installing new software, it's a good idea to back up your Mac.

1. From the Apple menu  in the corner of your screen:

• Choose System Settings. Then click General in the sidebar, and Software Update on the right.

• Or choose System Preferences. Then click Software Update.

2. If Software Update finds new software, click the Update Now or Upgrade Now button to install it.

3. Enter your administrator password, if asked. During installation, your Mac might restart, and you might see a progress bar or blank screen several times.

Cheers!