I did it without using a flow...
Figured out how to patch attachments from an item in one list to an item in a DIFFERENT list without using flow. If you need to patch attachments from an item in one SharePoint list to an item in a totally different SharePoint list, you must first remove the Attachments.Id parameter from the attachments collection!
I used the following code:
ClearCollect(colAttachments,AddColumns(DropColumns(colAttachments,"Id"),"Id",""));
ResetForm(AttachmentsForm);
//Alternatives to SubmitForm() commented out
//Patch(SharePointList,LookUp(SharePointList,ID=ThisItem.ID),AttachmentsForm.Updates);
//Patch(SharePointList,{ID:ThisItem.ID},AttachmentsForm.Updates);
SubmitForm(AttachmentsForm);
Why try to do PowerApps stuff directly in PowerApps instead of Power Automate?
Because
• It's faster
• It's easier to write the code that will work
• It's easier to maintain, edit, and improve the code that you write
• It's easier to debug code running directly in the canvas app, rather than having to send some data to Power Automate, to manipulate the data in Power Automate, to then send some response back to the canvas app, and finally to figure out why it's not working at first or why it stopped working later on
• It doesn't require any connectors (other than what's already in the app)
• It doesn't require making a Parent flow and Child flow so the user can run the parent flow which triggers a child flow which has connectors in Maker's context (I try to avoid adding dependencies on run-only user connections, which is what would be required for this to work in a flow that runs in the user's context)
• Did I mention it's faster? Yeah, a whole lot faster
Never do in Power Automate that which can be done in a canvas app (unless you don't have a canvas app or have some valid reason for not running the code directly in the app).
I have plenty of flows that need to be flows. I'd like to avoid superficially inflating that number because it's a form of technical debt. Figuring out how to do something directly in PowerApps is the low-code/no-code equivalent of code golfing. Power Automate is a way to cheap out on the intellectual rigor of learning PowerApps. If some code in PowerApps, like the one line I added to my solution above, gets the job done, then that's obviously preferable to adding a whole 'nother flow to my already overflowing list of flows.
Also, it's faster.
