Explanation:
Box 1.
We need to create a site and subnet for the remote site. The new site will be added to the Default IP Site Link so we don't need to create a new site link. You configure the replication schedule on the site link.
Box 2.
When we pre-create an RODC account, we can specify who is allowed to attach the server to the prestaged account. This means that the User1 does not need to be added to the Domain Admins group.
Box3.
User1 can connect the RODC to the prestaged account by running the AD DS installation wizard.
Reference:
https://mehic.se/2018/01/02/how-to-install-and-configure-read-only-domain-controller-rodc-2016/