We currently have a SharePoint 2019 On Premise Installation that has some custom list forms using SharePoint Designer, last night I found that I am no longer able to create any new forms or edit the existing forms using SharePoint designer 2013. My understanding from this support link is that Designer was turned off for SharePoint online, but from what I understand On Premise should be "supported" until 2026. I can find no documentation stating that this feature was turned off for On Premise during a patch. Can anyone confirm that this happened? Or can someone point me in the direction of a way to access my existing forms without breaking them (when I attempted to edit a form it completely broke it and I had to use ShareGate to copy the custom form back from our dev server).

