keychain not syncing across devices

Hi

I have a Macbook Pro (Big Sur 11.2), Iphone 11 Pro (IOS 14.4) and Ipad Pro IOS 14.4 and have always had iCloud Keychain so that password sync across devices. This has stopped working somtime in the last few months and I cannot figure out how to get syncing working again.

I have read that you can turn off iCloud keychain on all but 1 device, this one with the most up to date passwords, then turn back on and it will sync.

My problem is I do not have any one device that has all passwords and so do not know which to switch off.

Is ther a way to force the keychains to sync and merge, maybe with a script??

Thanks in advance for any assistance you can offer.

Regards

Ian