Ventura Duplicate calendar

After updating to Ventura (13.1) everything was fine, then yesterday I had to restart my iMac and noticed that all my email accounts had disappeared. So I signed back into my iCloud email account in the mail app and all my emails & folders downloaded from iCloud and everything looked fine.

Then I looked at my calendar. Every entry was duplicated. In fact in the Calendar sidebar I now have 2 iCloud entries each with the same list of calendars under them.

For the purposes of explaining my dilemma I will now call these "iCloud" and "Wrong"

"iCloud" entries are correct, they reflect the entries on my iPhone, iPad and the iCloud webpage itself. If I add an entry on one of these 3 it replicates across all 4 devices.

"Wrong" calendar entries only appear on the iMac. I cannot update the "iCloud" calendar on the iMac.

If I right click on "Wrong" or the "iCloud" calendar and follow the get info trail I end up at the same place : the internet account information in System Setting for my iCloud account. If I toggle the Calendar switch there to off, the "iCloud" calendar disappears from my iMac.

So how do I get rid of the "Wrong" Calendar, and bring back an "iCloud" calendar I can update on my iMac?

Any ideas?