Google Sync is a service which is authenticated by a Google password and does not go through SSO, so it will not be affected by switching SSO services.
iOS Sync and Android Sync go through SSO only with the first registration.
After the registration, account information will be held within devices or Google applications, so it will not be accessible by SSO.
Therefore, it will not be affected by SSO switching after the first registration.
■ What is Google Sync?
Reference Google page: https://support.google.com/a/users/answer/138740?hl=en
■ What is iOS Sync?
Reference Google page: https://support.google.com/a/answer/6328699?hl=en
■ What is Android Sync?
Reference Google page: https://support.google.com/a/users/answer/9013441?hl=en