Authentication issue while using Client Credential through Oauth2.0

I'm using powershell to access Graph.
I assigned only application permissions to the Entra registered App (not delegated permissions!)
So when connecting to Graph, no scope is needed.
But it only worked when I encrypted the access token:

You could test your App registration with powershell:

$body = @{
    grant_type    = "client_credentials"
    scope         = "https://graph.microsoft.com/.default"
    client_id     = $clientId
    client_secret = $clientSecret
}

$response = Invoke-RestMethod -Uri "https://login.microsoftonline.com/$tenantId/oauth2/v2.0/token" -Method Post -Body $body
$mgAccessToken = $response.access_token
$mgSecureAccessToken = ConvertTo-SecureString $mgaccessToken -AsPlainText -Force
$mg = Connect-MgGraph -AccessToken $mgSecureAccessToken