Please try this PowerShell:
#Parameters
$SiteURL = "https://wendytest123.sharepoint.com/sites/karley03"
$ListName = "Lib1"
$FolderServerRelativeURL = "/sites/karley03/Lib1/Folder1"
#Connect to SharePoint Online site
Connect-PnPOnline -Url $SiteURL -Interactive
#Get the Folder
$Folder = Get-PnPFolder -Url $FolderServerRelativeURL -Includes ListItemAllFields
#Update Folder's column
Set-PnPListItem -List $ListName -Identity $Folder.ListItemAllFields.Id -Values @{"CusColumn1" = "XXXXXXXXX"; "CusColumn2" = "XXXXXXX"} | Out-Null
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