I had Apple's Genius Bar over the phone bloke sort out some gremlins to do with backing stuff up. A process which included activating my cloud account which, co-incidentally or otherwise, resulted in the loss of a significant number of contacts from my contacts list.
ETA - Luckily, I have another (much older) iMac which is in no way connected to the new one and has historic versions of contacts as well as other stuff.
Big fan of Backblaze as an always on, backup everything system. Used it for about 10 years for laptop and 3TB of external drives (capacity is unlimited), only ever once had it throw up an error and that was easily solved without losing any data.
TBF, I'm an Apple fanboi, but only in the sense that I use both Windows and iOS because I have to and, ordinarily, I prefer iOS - but in this instance it disappoints.
I had Apple's Genius Bar over the phone bloke sort out some gremlins to do with backing stuff up. A process which included activating my cloud account which, co-incidentally or otherwise, resulted in the loss of a significant number of contacts from my contacts list.
ETA - Luckily, I have another (much older) iMac which is in no way connected to the new one and has historic versions of contacts as well as other stuff.