I was trying to use the method New-SelfSignedCertificate. Let say that I’ve used the example call from here: https://learn.microsoft.com/en-us/powershell/module/pki/new-selfsignedcertificate?view=windowsserver2022-ps

$params = @{
    Type = 'Custom'
    Subject = '[email protected],CN=Patti Fuller'
    TextExtension = @(
        '2.5.29.37={text}1.3.6.1.5.5.7.3.4',
        '2.5.29.17={text}[email protected]&[email protected]' )
    KeyAlgorithm = 'RSA'
    KeyLength = 2048
    SmimeCapabilities = $true
    CertStoreLocation = 'Cert:CurrentUserMy'
}
New-SelfSignedCertificate @params

First I’ve got this error:

New-SelfSignedCertificate : Parameter cannot be processed because the parameter name 'Subject' is ambiguous. Possible
matches include: -SubjectName -SubjectAlternative.

And I’ve changed Subject to SubjectName resulting:

New-SelfSignedCertificate : Cannot validate argument on parameter 'SubjectName'. The argument "[email protected],CN=Patti Fuller"
does not match the "^(CN|E|O|OU|C|ST|L):[^,:]+$" pattern. Supply an argument that matches "^(CN|E|O|OU|C|ST|L):[^,:]+$"
and try the command again.

Which actually matching the pattern. I’ve run similar command also few days ago and it worked correctly. I am using Windows 11