This was happening to me too, but I had a folder inside the iOS download folder set as my default folder. All downloads failed.
I selected the Orion folder and then I could download files again. I set it back to the folder inside the downloads folder on my iPhone and it's still working. Not sure what caused this, but luckily it's working again.
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App version: 1.3.19 (10) (WebKit 8621.1.15.10.7)
System version: 18.4.0
Device type: iPhone 13
Native bounds: (1170.0, 2532.0)
Scale: 3.0
Regular tabs: 17/orion://newtab/
Private tabs: 6/(