I have found three different fixes - it just depends on how extensive you want to get and the nature of your page and workflow.
Fix 1 - Simply rip out the copy file action, and replace it with the exact same action
Fix 2 - If your page is fairly simple (no custom components), then you can two a step copy - first copy the page to a different location, such as Style Library, and then copy the page from the Style Library to your Site Pages library
Fix 3 - If your page has custom components, Fix 2 will not work for you - in this case, you will need to create a child flow that does the copy file action, and then call that child flow from your main flow.
All three of these fixes have worked for different tenants, just depending on the nature of the workflow and page.
Something about the action has changed, and MSFT did your provide an abstraction layer for old actions - they simply updated the action and all new instances of the action will work, but old actions have to be replaced (which introduces the new code and/or config behind the scenes)
There's one other possible fix if nothing above works - I haven't tested this one. You could call an Azure Runbook that uses PowerShell to copy the page. Again, quite the workaround, but it should work.