Programmatically "Apply label to items in this list or library"

In the end I resorted to PowerShell:

try
{

    $listId = (Get-PnPList "Shared Documents").Id

    $ie = New-Object -com InternetExplorer.Application 

    try
    {
        $applyLabelUrl = "$($spUrl)/_layouts/15/Hold.aspx?Tag=true&List={$($listId)}"
        Write-Host $applyLabelUrl

        $ie.visible = $true
        $ie.navigate($applyLabelUrl)

        for ($i = 0; $i -lt 300; $i++)
        { 
            if ($ie.ReadyState -eq 4) { break }

            Start-Sleep 1

            if ($i -eq 299) { throw "Unable to start IE session to simulate HP RM turning off inheritence." }
        }

        Start-Sleep 2

        $complianceTagDropDown = $ie.Document.getElementByID('ctl00_PlaceHolderMain_inputFormSectionMain_ctl01_ComplianceTagDropDown')
        if ($complianceTagDropDown.id -ne "ctl00_PlaceHolderMain_inputFormSectionMain_ctl01_ComplianceTagDropDown")
        {
            throw "Didn't get assurance that I found complianceTagDropDown"
        }
        else
        {
            $isFound = $false

            for ($i = 1; $i -lt $complianceTagDropDown.options.length; $i++)
            { 
                if ($complianceTagDropDown.options[$i].text -eq $labelName)
                {
                    $complianceTagDropDown.options[$i].selected = $true
                    $isFound = $true
                    break
                }		
            }

            if ($isFound -eq $false)
            {
                throw "Unable to select '$($labelName)' in complianceTagDropDown. No such option?"
            }


            $saveButton = $ie.Document.getElementByID('ctl00_PlaceHolderMain_ctl00_RptControls_btnOK')
            if ($saveButton.id -ne "ctl00_PlaceHolderMain_ctl00_RptControls_btnOK")
            {
                throw "Didn't get assurance that I found saveButton"
            }
            else
            {
                $saveButton.click()
            }

        }

    }
    finally
    {
        $ie.Parent.Quit()
        Start-Sleep 1
    }
}
finally
{
}