20*2.1 = 42, so it will depend on the LED's selected. Get something that's adustible, say +-10%. e.g. https://www.mouser.com/Power/Power-Supplies/AC-DC-Power-Modules/_/N-dv0g5?P=1yxt77s

=(48+4.8)/20 is 2.64 V per LED, so it's still pretty tight. There is a voltage drop across the OPTO too to consider as well. Two strings of 10 might be better.

You could series connect a 48V and a 12V supply for a 60V supply or slightly less. take 10% off of each.

 

You have LED brightness to contend with. Use Vf to select.

You have current drive and voltage headroom to contend with on the input. https://www.analog.com/en/products/lt6700.html may help. Use a resistor instead of an opto. There is a single comparitor in the series too.

The ULN2003 might help. There is an 8 channel counterpart.

If you do LEDS in series, you may max out available power supplies like 48V.

OPTOMOS relays only need about 1mA, but they are expensive.

High side or low side drivers might help too.

 

here's https://www.analog.com/en/products/ltc7001.html#product-overview a high side driver you might be able to use.

OPTOMOS relays are really cool because of only needing 1 mA to operate. An example: https://www.digikey.com/product-det...cuits-division/CPC1017NTR/CLA233CT-ND/1212844

Thus, it would be easy to get two or more decent outputs.