lol ask autowiz about the prusa mmu - 'total nightmare' would be how i describe his experience.

forget sls - that's $10,000 absolute minimum.

A resin machine using 'tough' or 'flexible' resin would be your easiest bet.

depending on the file, wall thickness, text size etc.
an IDEX fdm machine could probably do it.

Using 0.15mm nozzles - not easy to use and be prepared for it to take 4-6 hours per key cap.
personally I don't believe that any current fdm printer can reliably pull of sub 0.05mm layers.
though if you were going to do it - then a teeny tiny nozzle diameter would probably help.

what sort of actual sizes are you looking at ?