Glock 43 aluminum slide ?

Never heard of it.
Show a link.

https://www.sportsmansoutdoorsupers...with-cerakote-purple-frame-and-aluminum-slide

Could have been that, in which case "aluminum" refers to the color of cerakote finish on the slide

Or it could have been referring to an aluminum slide cover plate.

Clear at the bottom under firearm specifications it says:
Frame Finish: Purple Cerakote
Slide Finish : Aluminum Cerakote

Aluminum refers to the color of the slides finish, not what the slide is made from

Glock custom colors.

An aluminum slide would beat the gun to pieces. To light. The spring would have to be so heavy that it would be almost impossible to pull back