In the unstable development version 5.99 there’s a project wide board setting for edge clearance, but not for each layer. Layers are handled by textual design rules, see Need some guinea pigs for a rule-based DRC <<PROTOTYPE>>.
If you really need different clearance for different layers I think you are out of luck with v5.1. But if 0.4mm for all is enough it has a workaround: set the width of the edge.cut lines. The actual board edge is always in the middle of the line (as is a convention in the industry) but KiCad takes the outer edge of the line to consideration when calculating the clearance. Some manufacturers don’t like thick outlines and especially if they aren’t all of the same thickness, but most would accept it anyways.