Calendar Sync issue - Calendars on Mac not showing in Finder and vice versa

After multiple helpdesk chat and phone calls to no avail, I'm hoping someone in this forum may be able to help. A few weeks back my 'old' Mac and iPhone stopped syncing properly and I had multiple versions of the same entry showing up (up to 48 in one case) for no apparent reason. It's my busiest time of year and I couldn't be without either device so I decided to bite the bullet and buy new. I now have a new MacBook Pro and a new iPhone 16 Pro both running latest OS and up to date.

I backed up the old Mac, then used Migration Assistant to bring over the data to the new Mac. All good so far. HOWEVER... the list of calendars in "Finder" is not current. I failed to 'merge' the calendars and had different versions on the phone, the Mac and the Cloud. I have:

• MANUALLY, compared data on the phone to the Mac, ensured all events on iPhone were entered to the Mac so I know that calendar is correct.
• MANUALLY, compared data on the cloud to the Mac, ensured all events on Cloud were entered to the Mac so I know that calendar is complete and correct.
• Deleted calendars from my phone (including deleting the app and reinstalling it)
• Deleted calendars from iCloud and
• switched off the sync to cloud on both iPhone and Mac leaving only "mail" switched on.

So currently my 'single source of truth' for calendars is "on my Mac".

The list of calendars in "Finder" is different from the calendars I can see "on my Mac" - some, but not all, have the same names and entries on those are incomplete when compared to the Mac calendars so it looks like they're historic. Yes, I did do a replace on device, pulled them to my phone and then manually compared them back to the Mac entries to confirm they were incomplete.

It appears to me that wherever "Finder" is looking, is the wrong place. I would like to find out where its looking and delete the data from that location to get rid of the 'obsolete' calendars. I then need to find out where the 'On my Mac' calendars are and either transfer them to where "Finder" is looking, or get "Finder" to look at where they located.

I have already tried:

• boot in safe mode - issue recreated;
• create new admin profile - create new calendar - Finder still sees 'old' calendars not new calendar on new profile;
• boot in safe mode using new admin profile - issue recreated;
• restore software on Mac - issue recreated;
• Sync to old iPhone from new Mac to check it's not the phone - issue recreated.

The issue is definitely the Mac not the phone as the manual sync is working, just not with the right data.

It appears to me to be either Finder is looking in the wrong place, or there's some form of cache that needs to be cleared to let it "see" the calendars that are 'On my Mac' rather than the ones it thinks are there.

I see from a search that a few people have raised similar issues over the past couple of years but none of the responses seem to have fixed things as it seems to ask them to check the standard stuff which doesn't help. It may be that others weren't aware that Finder and On My Mac were not aligned on location if they hadn't renamed some of their calendars and therefore maybe I'm further on in identifying the issue than they were.

I don't want to have to manually type in all the entries to the phone, and even if I do, it's still not going to remain in sync unless I do that every day for every entry - which is not an option.

Any genius out there know how I can fix this to get the whole thing working properly again?