When a PDS 11 fires on an active player moving in an adjacent space and scores a hit, can a fighter be destroyed or does it need to be a non fighter unit? (not referring to advanced fighters)
Anytime a PDS scores a hit, regardless if it's an upgraded or regular PDS, the active player decides which ships should be destroyed. The active player being the person moving their ships. This could be a fighter unit if they have them. All ship units are "units" in terms of space combat, cannon or ship to ship.
The rules for this game is pretty comprehensive. For more information regarding PDS please read over the Twilight Imperium 4 Wikipedia - Space Cannons. Additionally, you may view page 22 of the reference guide, subsection 66.2 labelled Space Cannon Offense.