Hello

I have a single wall light switch which operates two lights in a big room.

I would like to now separate this one switch and have the two lights operate on two separate switches. At this point there is two red wires and one white wire operating the one switch.

Please let me know if I can separate the into two switches and operate with a dimmer. Kindly advise your instruction

Is wiring in conduit? if so, an additional switchleg would allow separating.
If romex, you need to get a cable from switch location to the easiest light to get too. Use existing for the long or difficult run.
IF the box is 4X4" you may be able to carefully cut drywall? And install a 2 gang mudring for 2 devices.
They make a dimmer that has 2 sliders for 2 light controls that fits a single device.