Contacts don't sync between have en Apple Devices

Hello! I remembered that when I initially tried this there were duplications of my missing 50 contacts now contained in my iCloud account and it required me to monkey-around a little bit. Next, I then used the Contacts function "Look For Duplicates" which then deleted the dupes within iCloud. On my Mac I then disabled the Contacts iCloud account and re-enabled, then all synced together with the same amount of contacts within iCloud, iOS & macOS. Not sure why it does what it does, perhaps these contacts' data were corrupted but all now has stayed in-sync several weeks now.....

Try going to System Preferences/iCloud and stop Contacts syncing by unchecking the box. Wait a couple of minutes, then check syncing.

Contacts, Calendars, or Reminders - Get help using iCloud

Last resort - have you tried signing out of iCloud and then sign back in?

Hello! I had this same problem with my Mac Laptop not syncing Address Contacts with my iCloud account as well. Contacts between iOS devices would sync together but found 50 contacts NOT synced between my Mac & iCloud. Initially tried signing out of iCloud and back in with no resolve. Did recently, re-installed macOS due to other issues of performance but still had same problem syncing contacts prior and afterwards. Ultimately, what I did find to correct the issue was to EXPORT my Contacts from iCloud which then opened the IMPORT Function on my Mac's Address Book. I then selected the icon (which is on the top row, last icon on right side of Import Window) to Import the missing Contacts. This function then imported the missing 50 Contacts. Tested syncing function by Uploading from my Mac a new Contact and then deleting it from my iCloud Account. All appears normal at this time. Any questions let me know....!

Tried it. Didn't work. I'm not sure what else to do get iMac calendar/contacts to sync with iphone and ipad. It does say that it syncs but the information does not sync.

Try going to iCloud.com using a computer to see if the items are there and whether they are from the device or the computer. That should show whether the device or the computer isn't syncing. If the computer, try going to System Preferences/iCloud and stop syncing. Wait a couple of minutes, then recheck syncing. If the device, go to Settings/Your Name/iCloud and do the above. As a last resort, you can also try signing out of iCloud and then sign in again.