I did that as per Apple Support:
To restore your missing calendars:
- Sign in to iCloud.com.
- Scroll down to the bottom of the window, then select Data Recovery.
- Select Restore Calendars.
- Select Restore next to the date before you deleted the content.
- Select Restore again to confirm.
... did not work ... so I did the following as per Apple Support:
- macOS 13.3 or later: Choose Apple menu > System Settings, click [your name] at the top of the sidebar, then click iCloud. Below Apps Using iCloud, click Show All or Show More Apps, then turn on Calendars.
It was already "on"... so , I turned it off waited a few seconds, turned it back on .... and everything was restored.
It sounds very complicated but it work. Hope the same for you.