Conditional Access policy: Block access for unknown or unsupported device platform

1. Sign in to the Microsoft Entra admin center as at least a Conditional Access Administrator.
2. Browse to Protection > Conditional Access.
3. Select Create new policy.
4. Give your policy a name. We recommend that organizations create a meaningful standard for the names of their policies.
5. Under Assignments, select Users or workload identities.
   1. Under Include, select All users
   2. Under Exclude, select Users and groups and choose your organization's emergency access or break-glass accounts.
6. Under Target resources > Cloud apps > Include, select All cloud apps.
7. Under Conditions, select Device platforms
   1. Set Configure to Yes.
   2. Under Include, select Any device
   3. Under Exclude, select Android, iOS, Windows, and macOS.
   4. Select, Done.
8. Under Access controls > Grant, select Block access, then select Select.
9. Confirm your settings and set Enable policy to Report-only.
10. Select Create to create to enable your policy.

After administrators confirm the settings using report-only mode, they can move the Enable policy toggle from Report-only to On.