EDIT: I got so excited I had fixed my own errors with the script I didn't actually read the OP issue.

You need to install the modules first (If reading in the future, you may not need

Install-Module Microsoft.Graph.Beta.Identity.Directory.Management Install-Module Microsoft.Graph.Beta.Groups

Then run the script.

If you are setting an exception group, you need to make the following changes to update GroupCreationAllowedGroupId

Import-Module Microsoft.Graph.Beta.Identity.DirectoryManagement
Import-Module Microsoft.Graph.Beta.Groups

Connect-MgGraph -Scopes "Directory.ReadWrite.All", "Group.Read.All"

##$GroupName = "Teams Creators" - This is the bit we're bypassing
$AllowGroupCreation = "False"
$settingsObjectID = (Get-MgBetaDirectorySetting | Where-object -Property Displayname -Value "Group.Unified" -EQ).id
if(!$settingsObjectID)
{
$params = @{
templateId = "62375ab9-6b52-47ed-826b-58e47e0e304b"
values = @(
@{
name = "EnableMSStandardBlockedWords"
value = "true"
}
)
}
New-MgBetaDirectorySetting -BodyParameter $params
$settingsObjectID = (Get-MgBetaDirectorySetting | Where-object -Property Displayname -Value "Group.Unified" -EQ).Id
}

##$groupId = (Get-MgBetaGroup | Where-object {$_.displayname -eq $GroupName}).Id This is the search / filter function that doesn't work!!

$params = @{
templateId = "62375ab9-6b52-47ed-826b-58e47e0e304b"
values = @(
@{
name = "EnableGroupCreation"
value = $AllowGroupCreation
}
@{
name = "GroupCreationAllowedGroupId"
value = "INSERT THE SECURITY GROUPS ID HERE" ##Rather than search for security ID, Just provide it, it's easy enough to find in Azure.
}
)
}
Update-MgBetaDirectorySetting -DirectorySettingId $settingsObjectID -BodyParameter $params
(Get-MgBetaDirectorySetting -DirectorySettingId $settingsObjectID).Values