The customized form simply does not retrieve the param value:
Looking at the browser source when I browse to the SharePoint list, I can see that the form is embedded in an iframe. So I mashed up a URL based in the information I found in browser source, and browsed to the customized form using a similar URL:
This means that if we want to pass information to a PowerApps form from another part of SharePoint (e.g. from a page added to SharePoint or a custom Document Set page), we either have to:
Browse to the form using the "web.powerapps.com", by looking at the source of the SharePoint list page to get the App ID. This will be confusing for the user.
Having the "Param" function not work in a SharePoint custom form seems to be a big gaping hole. Can this be fixed please?