How to sync contacts in 53 android phone and iphone?

Question

iPhone

There are 53 phones, some for android and some for Iphone. How can I synchronize contacts between them. A Google account is ideal, but there is a limit of 10 devices per account. THE TASK is to synchronize not all contacts in the phone, but only certain ones.

For those who are in the tank.
Example. In addition to the main Google account on the phone, there are 2 for syncing between devices. and those contacts that need to be synchronized are saved to the second account. Everything spoils the limit of 10 devices. And we have 53 of them. I would be grateful for an answer, and reasoning, perhaps your reasoning will push you to the right thought. Thanks

Answer 1

nextcloud or rather use WebDav (it is not necessary to use nextcoloud as a provider) to store contacts and use the appropriate software for this
dock for ios
dock for android