A mild soap and a classic cheap sponge do the trick for me. Occasionally if the filament left some traces on the plate, instead of using too much elbow grease and avoid contaminating the sponge with filament residues, I use a dishwashing brush like the one in the picture. In my area they come with different softness like toothbrushes. Medium is usually enough. I tried to find a picture without any logo on them. These look cheap but a quality one lasts for a very long time, does not scratch and easy to rinse. It is much safer than those abrasive alternatives like scotch brite or Stainless Steel scrubbers.
The brushes with handles or nail brushes are much harder than these ones and i assume they can sand away the grits of the plate. Idk for sure as i did not tried them on build plates at all, though I saw them scratching non stick pans.
