Hi @tsunatsuna ,
Which control do you want to display the control? Display Form?
If you want to click the file in form and open it, the Launch function can be useful to open the file online or in client apps.
However, the Attachment control in the Attachment Data Card is a standard control designed to add, remove, download the attachment files and have no OnSelect property to set. We just try to delete it, and add a list box instead in the data card.
1. set Items property of listbox as below to display all files
ThisItem.Attachments
2. set OnSelect property of listbox as below to open the files online.
Launch(ListBox1.Selected.AbsoluteUri & "?web=1")
3. To two errors, just delete Update property and set Y property properly.
If you want to open the file in client apps, just put 'ms-excel: ofe|u|' (for excel files), or put 'ms-word: ofe|u|' at the beginning of the link. So change OnSelect property of list box as below, then open excel/word files in client app, open other files online.
If(".xls" in ListBox1.Selected.DisplayName,Launch("ms-excel:ofe|u|"&ListBox1.Selected.AbsoluteUri),".doc" in ListBox1.Selected.DisplayName,Launch("ms-word:ofe|u|"&ListBox1.Selected.AbsoluteUri),Launch(ListBox1.Selected.AbsoluteUri & "?web=1"))

Hope this helps.
Best regards,
Sik
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