Hello @Jason Levy ,
You could use PnP powershell to achieve this, below is my example script for your reference:
$siteURL="https://tenant.sharepoint.com/sites/test"
$library="/Shared Documents"
Connect-PnPOnline -Url $siteURL
$folderColl=Get-PnPFolderItem -FolderSiteRelativeUrl $library -ItemType Folder
foreach($folder in $folderColl){
$folderUrl=$library+"/"+$folder.name
Add-PnPFolder -Name "2021" -Folder $folderUrl
}
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