Merge pull request #233036 from Justinha/sys-mfa-preview

added known issue for CBA

Author: prmerger-automator[bot]

articles/active-directory/authentication/concept-system-preferred-multifactor-authentication.md

@@ -4,7 +4,7 @@ description: Learn how to use system-preferred multifactor authentication
 ms.service: active-directory
 ms.subservice: authentication
 ms.topic: conceptual
-ms.date: 03/22/2023
+ms.date: 03/31/2023
 ms.author: justinha
 author: justinha
 manager: amycolannino
@@ -86,9 +86,9 @@ Content-Type: application/json
 }
 ```
 
-## Known issues
+## Known issue
 
-- [FIDO2 security key isn't supported on mobile devices](../develop/support-fido2-authentication.md#mobile). This issue might surface when system-preferred MFA is enabled. Until a fix is available, we recommend not using FIDO2 security keys on mobile devices. 
+[FIDO2 security keys](../develop/support-fido2-authentication.md#mobile) on mobile devices and [registration for certificate-based authentication (CBA)](concept-certificate-based-authentication.md) aren't supported due to an issue that might surface when system-preferred MFA is enabled. Until a fix is available, we recommend not using FIDO2 security keys on mobile devices or registering for CBA. To disable system-preferred MFA for these users, you can either add them to an excluded group or remove them from an included group.
 
 ## Common questions