When we have a tenant, where AIP and Data Labels have not yet been configured and you wand to create a new Data Sensitivity Label in the https://compliance.microsoft.com Admin Console and define the scope you will see that the option “Group and Sites” is greyed-out:

In order to activate it, open a PowerShell as an Administrator and start the following cmdlets
Install-Module AzureADPreview

Note: Since the AzureADPreview Module has some conflicting cmdlets with the module AzureAD, which you most probably (and rightly so) have already installed on your client, you can open a Windows Sandbox App on your client.
to do this go to the Windows Features, and activate the “Windows Sandbox” Feature:

Then Reboot the client and Start the Sandbox:

You can now start your PowerShell session inside as an admin and install the Module
Then type:
Import-Module AzureADPreview
Connect-AzureAD
#You'd need to Authenticate as a Global Admin here
$setting = (Get-AzureADDirectorySetting | where -Property DisplayName -Value "Group.Unified" -EQ)
$template = Get-AzureADDirectorySettingTemplate -Id 62375ab9-6b52-47ed-826b-58e47e0e304b
$setting = $template.CreateDirectorySetting()
#Display the current group Settings
$Setting.Values
Note that the Option “EnableMIPLabels” has a Value of “False”

Then type:
$Setting["EnableMIPLabels"] = "True"
New-AzureADDirectorySetting -DirectorySetting $setting
Type again $Setting.Values and note that the value has changed now:

If you’re receiving a Request_BadRequest error, it’s because the settings already exist in the tenant, so when you try to create a new property:value pair, the result is an error. In this case execute in PowerShell the following code:
$grpUnifiedSetting = (Get-AzureADDirectorySetting | where -Property DisplayName -Value "Group.Unified" -EQ)
$Setting = $grpUnifiedSetting
$grpUnifiedSetting.Values
$Setting["EnableMIPLabels"] = "True"
$Setting.Values
Set-AzureADDirectorySetting -Id $grpUnifiedSetting.Id -DirectorySetting $Setting
You should be now able to activate the option when creating a new Sensitivity Label

After the Change is done, you need to sync the labels, so that they are visible in SPO and M365
In PowerShell execute the following:
Install-Module ExchangeOnlineManagement
Connect-IPPSSession -UserPrincipalName <Your Global Admin Account>
Execute-AzureAdLabelSync