According to the Microsoft SC-300: Identity and Access Administrator Study Guide, the enforcement of Modern Authentication for Microsoft 365 services such as Exchange Online is achieved through Conditional Access policies. Conditional Access allows you to block legacy authentication protocols (such as POP, IMAP, SMTP, and MAPI over HTTP) that use Basic Authentication, and require Modern Authentication (OAuth 2.0) instead.
Microsoft Learn explains that you can configure a policy that "blocks access requests using legacy authentication clients" under Conditions # Client apps and select "Other clients (legacy authentication clients)" to enforce Modern Authentication. Defender for Cloud Apps OAuth policies and Intune app
/compliance policies do not control authentication protocols at the tenant level.