Same as CodyBrooks. Got this error trying to start install on external SSD, only was able to continue after formatting as APFS.

I'm seeing same thing in my own app, and tried Photos as well with same behavior. Repro Open Photos Select a Photo Share button (lower left) Scroll to "Export Unmodified Original" Select Export Unmodified Original See "Save" button dimmed. Try to create a new folder -> Doesn't work