I read that as being figurative, i.e. Pergamos was a place of great wickedness.
Can't see much reason for the devil to have a literal, physical throne on earth.
Thanks for the cite.
God’s word has made it plain that Satan has had a continuous physical throne here on Earth.
It has been at various places, such as Ninevh (AKA Babylon),
Tyre, Pergamos, and Rome. He is the ‘Prince’ of the Earth. That will be so until the physical return of the Lord, at which time he is to be placed in ‘chains.’
Satan has dedicated servants here, just as Christ does.