et-PnPWebhookSubscriptions fails with 'The attempted operation is prohibited because it exceeds the list view threshold'

[RSCA001]

Get-PnPWebhookSubscriptions -List $mylist
where $mylist is a folder fails with the following message

The attempted operation is prohibited because it exceeds the list view threshold.

I have seen that error message in the past when trying to work with a list with 5000 items in it. This folder has 19 documents and 2 webhooks ,

Does anyone know how to get to the bottom of this?