[evilbib]

if event == "PLAYER_ENTERING_WORLD" then
        C_Timer.NewTicker(0.1, function(self)
            local SkadaDisplayBar = Skada.displays["bar"]
            if not SkadaBarWindowDamage then 
                return
            end
            SkadaBarWindowDamage:CreateBeautyBorder(12)
            hooksecurefunc(SkadaDisplayBar, "AddDisplayOptions", function(self, win, options)
                options.titleoptions = nil
                options.windowoptions = nil
            end)
            hooksecurefunc(SkadaDisplayBar, "ApplySettings", function(self, win)
                local skada = win.bargroup
                skada:SetBackdrop({ 
                    bgFile = "Interface\\Tooltips\\UI-Tooltip-Background", 
                    edgeFile = nil, tile = false, tileSize = 0, edgeSize = 32, 
                    insets = { left = 0, right = 0, top = 0, bottom = 0 }
                })
                skada:SetBackdropColor(0, 0, 0, 0.8)
            end)
            self:Cancel()
        end, 1e4)
    end

This is what I have now and it works.

But still I wonder why it stopped working all of a sudden, I also tried older Skada versions.