Hi @Glenn Skinner
I will recommend you to use pnp powershell to reach your requirement. Please refer to following code
#Parameters
$SiteURL = "https://xxx.sharepoint.com/sites/test"
$ListName = "SPDocuments"
$CreatedBy= "xxx@xxxx.com"
#Connect to PnP Online
Connect-PnPOnline -Url $SiteURL -Interactive
#Get the all subfolders in folder A
$folders = Get-SPOFolderItem -FolderSiteRelativeUrl "/SPDocuments/2022/A" -ItemType Folder
#Update document properties
foreach($folder in $folders){
Set-PnPListItem -List $ListName -Identity $folder.Id -Values @{"Author" = $CreatedBy}
}
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