To check if Microsoft Team creation is restricted to a security group run the following PowerShell:

# Uninstall Azure AD module
Uninstall-Module AzureAD
# Install the latest AzureADPreview module
Install-Module AzureADPreview
Connect-AzureAD
$settingsObjectID = (Get-AzureADDirectorySetting | Where-object -Property Displayname -Value "Group.Unified" -EQ).id
$groupSettings = (Get-AzureADDirectorySetting -Id $settingsObjectID)
$groupSettings.Values

In the output check if the value EnableGroupCreation is set to false. This will restrict Team creation to a security group. The value GroupCreationAllowedGroupId specifies which security group has access to create Teams.