Does Probopass' "Magnetic Pull" attack do 40 damage if the opponent cannot switch their Active Pokemon to the Bench or if the Bench is empty?
If you cannot switch the opponent's Pokemon there is no "new Active Pokemon" to be damaged, so no damage is done.
Source: Brilliant Stars FAQ; TPCi Rules Team (2022-02-24)

Relevant cards

Note: All applicable cards may not be listed below.
SWSH9_99
SWSH9_99