Hi @SDonaghy ,
How do you auto-fill the Edit form based on the value selected within the ComboBox? Could you please share a bit more about the formula?
Does the Edir form connect to your new "Confirmed Reviews" List? Do you set up a variable to store the attachments value from the record (find this record based on the selected value within the ComboBox) in your original SP List?
Based on the needs that you mentioned, I afraid that there is no way to achieve your needs within PowerApps currently. Currently, within PowerApps, you could only manually attach files within the Attachments control to upload to your SP List. Binding the Attachments to a variable (contains Attachments data) is not supported to upload files back to SP List.
As an alternative solution, I think the combination of Microsoft Flow (Power Automate) and PowerApps could achieve your needs. I have made a test on my side, please consider take a try with the following workaround:
Flow's configuration as below:


App's configuration as below:

Set the OnSuccess property of the Edit form to following:
'PowerApp->OriginalListItemID,NewSubmittedListItemID,Getat...'.Run(First('20190816_case6').ID, Form1.LastSubmit.ID);
ResetForm(Form1)
On your side, you may type:
'YourFlowName'.Run(
LookUp('Your Original List', FilteredColumn = ComboBox.Selected.Value, ID), // Find the List Items ID of the record from your Original List based on the selected value within the ComboBox
EditForm1.LastSubmit.ID
);
ResetForm(Form1)
Please take a try with above solution, check if it could help in your scenario.
Note: When you use above alternative solution, it is not necessary to enable the Attachments field within the Edit form, instead, the flow could this needs.
More details about firing a flow from a PowerApps app, please check the following article or video:
https://docs.microsoft.com/en-us/powerapps/maker/canvas-apps/using-logic-flows
https://www.youtube.com/watch?v=1wl9AtxWdkg
Best regards,