I really liked the Prusa Mk3 Dust Tray, Toolbox, Filament Oozing Collector by GeorgeZSL on my MK3, but it didn't fit my new MK4 so I adjusted the back end in 3D Builder so now it fits well.
Fits on both sides, you just need to mirror in in your slicer..
The author remixed this model.
Adjusted with width of the “pocket” in the back of the tray and reduced the heigh so it fits the mounts in the MK4.