Can a user attach a file in a transaction, when the role doesnt have permission to edit the transaction?

yes, files can be added on the view screen

I want to disagree with this - that it's not possible. However, my memory could be failing me here.

I have a rol with "Create" permission on Lists > Docs and files, and view permission on the record itself. But the buttons to attach are not shown in the Files subtab 😞

and if you change it to edit - the buttons get added, right?

I'm pretty sure you cant attach files without edit permission to the transaction

We use this in journal entries in our system that have create permission only but cannot edit or approve, but can add files after saving. I'll poke around and see if I can figure the settings we set for that.

I mean, easiest way would be to give edit, and then lock the record with workflow conditionally.