If you attempt to connect to a Remote Desktop Connection (RDP) that is not a domain joined computer you may get the following error:

Your credentials did not work Windows Defender Credential Guard does not allow using saved credentials

To resolve the issue you must follow these steps:

1. Find the Saved Credentials
2. Delete the Saved Credentials
3. Recreate the Credentials with Generic Type

Find the Saved Credentials

To list all RDP Saved Credentials run the following command:

cmdkey /list:TERMSRV/*

Currently stored credentials for TERMSRV/*:

    Target: TERMSRV/print.domain.internal
    Type: Domain Password
    User: dom\john.doe
    Local machine persistence

    Target: TERMSRV/dc1.domain.internal
    Type: Domain Password
    User: dom\john.doe
    Local machine persistence

Or run this command to find the saved credentials for a specific server name or IP address:

cmdkey /list:TERMSRV/<targetNameOrIp>

Examples:

cmdkey /list:TERMSRV/server.domain.com
cmdkey /list:TERMSRV/127.0.0.1

Delete the Saved Credential

Remove the saved credentials that are causing the issue. You can do this by using the following command in Command Prompt or PowerShell:

cmdkey /delete:TERMSRV/<targetNameOrIp>

Replace <targetNameOrIp> with the appropriate target name or IP address for your Remote Desktop Connection (RDP).

Recreate the Credentials with Generic Type

Recreate the credentials using the cmdkey command with the /generic flag. This ensures that the credentials are compatible with Credential Guard:

cmdkey /generic:TERMSRV/<targetNameOrIp> /user:<username> /pass

Replace <targetNameOrIp>, <username> with the correct values for your RDP connection. Note that passwords saved through the RDP UI end up as “Domain” type credentials and aren’t compatible with Credential Guard. However, passwords saved through cmdkey /generic end up as "Generic" type and work with Credential Guard enabled. </code<username>>

References:

https://superuser.com/questions/1756354/windows-defender-credential-guard-does-not-allow-using-saved-credentials-for-r

https://www.techtutsonline.com/windows-defender-credential-guard-does-not-allow-using-saved-credentials/