No, I mean real good old sliding skirt (= skirt that is sliding up and down in its channel) like the one we see at the right bottom or the one that was removed in the short video "Williams tests a no-suspension F1 car to improve its ground effect ".
Sliding skirts banned and 6cm ground clearance regulations enforced, these were sidestepped by Brabham using a hydro-pneumatic chassis lowering ploy, which was subsequently copied by all. Suspension travel minimised to maintain consistent download. Flexi skirts were used instead.
New flat-bottomed regulations applied, virtually banning ground effects and under wing profiles between the complete wheels.
So again, who was the last GP winner with sliding skirts ? And it's true it's not Alan Jones at Watkins Glen in 1980.