Display Name Spoofing very often recently - how to prevent it

For DisplayName spoofing you definitely want User Impersonation protection, and you can only protect up to 350 users (per Anti-Phish policy, not sure if/how well it scales up if you try to do as many policies as necessary to cover all users).  User Impersonation Protection

You'll get more than just DisplayName spoofing protection.  Even similar email addresses will be detected.  You will likely need to then add some Trusted Senders as well, to avoid certain external senders being falsely detected as impersonation attemps.  Trusted Senders and Domains

To close the loop on Domain Impersonation - that is focusing on the domain portion of the email address, so it is not going to cover you for DisplayName spoofs.  Things like M1crosoft.com would be detected as impersonating Microsoft.com.