Unable to access external HD

I'm trying to save something on my external HD, but I get this error:

Unable to access "TOSHIBA EXT"

Not authorized to perform operation (polkit authority not available and caller is not uid 0)

I made a snapshot of the error window, but that doesn't go to well either. I would say, this is enough information to help me out. If not, we'll see later.

I use Ubuntu 20.10

Leon