Contacts not restoring from backup on iPhone and iPad after iOS 18 update

after i updated my iphone 15 and iPad pro to ios 18, 3100 contacts vanished (out of 770). They still exist on my MacBook air (which i updated to MacOs 15).

I tried restoring my iPhone contacts from a backup predating the ios 18 install, which took effect on the Macbook. but not on the iPhone.

i signed out of cloud and deleted contacts from the iPhone (twice). when it re-synced, i still had 460 contacts.

I did all of this with apple support and they had no solution.

I only sync contact with iCloud, no other services. Both iPhone and iPad lost contacts (the same number and seemingly the same ones).

Thus far, Apple support suggested that I should have waited to update to an OS until the .1 update is released. I found this unhelpful, as 18.0 is the official release.

Any suggested on how i get all of my contacts to sync from my MacBook or restore from my backup?

Thanks

[Re-Titled by Moderator]