Hi,@Camacho
Thanks for posting your question in the Microsoft Q&A forum.
When adding an Exchange 2016 server to a domain with an existing Exchange 2010 server, it is indeed necessary to install the Mailbox role on the new Exchange 2016 server. This role is essential for hosting mailboxes and public folders and is a requirement if you're planning to migrate to Office 365.
Regarding the warning about Exchange 2013 roles, you don't need to be concerned if you're not using Exchange 2013. This message is informing you that once you install Exchange 2016, you won't be able to install Exchange 2013 in the same environment. This does not affect your existing Exchange 2010 setup. It's a standard warning to ensure that you're aware of the installation's implications on future role installations. As long as you're planning to go from Exchange 2010 to Exchange 2016 and then to Office 365, you can proceed with your installation.
If my answer is helpful to you, please mark it as the answer so that other users can refer to it. Thank you for your support and understanding.