Use SharePoint online Management Shell to activate the feature.
To identify the exact feature ID, we need to browse the manage site features ro site collection feature page and inspect the specific feature button in browser developer tools using F12 and grab the unique GUID.
use that in the powershell with example as shown below:
Import-Module Microsoft.Online.SharePoint.Powershell
$siteurl="https://sitecollectionurl.sharepoint.com/sites/testsite"
[Microsoft.SharePoint.Client.ClientContext]$clientContext = New-Object Microsoft.SharePoint.Client.ClientContext($siteurl)
$username="[email protected]"
$secure_string_pwd = convertto-securestring "yourpassword" -asplaintext -force
$clientContext.Credentials = New-Object Microsoft.SharePoint.Client.SharePointOnlineCredentials($username, $secure_string_pwd)
$site = $clientContext.Site;
$featureguid = new-object System.Guid "f6924d36-2fa8-4f0b-b16d-06b7250180fa"
$site.Features.Add($featureguid, $true, [Microsoft.SharePoint.Client.FeatureDefinitionScope]::None);
$clientContext.ExecuteQuery();
Reference blog for more details