Will it hold a 34-inch curved ultrawide?

Yes, if the monitor weighs 28.6 lbs or less. Curved panels have a lower per-arm limit than flat ones, so check the spec sheet weight before mounting.

Does it fit a 38-inch monitor?

The arm is rated to 38 inches, but a 38-inch ultrawide often weighs more than the 28.6 lb curved limit. A lighter 38-inch flat panel within 35.2 lbs is fine.

Clamp or grommet: which should I use?

Both hardware sets are included. Use the clamp on most desks and the grommet mount when you can drill or use an existing hole and want the cleanest look.

Can each arm be positioned independently?

Yes. Each arm has its own gas spring, tilt, swivel and pivot, so you can set different heights and put one screen in portrait.

Does the RGB need special software?

The lighting runs through the arm's own connection and can be controlled without a full MSI ecosystem, though MSI's software gives more lighting options.

How much desk depth does it need?

The clamp needs a few inches of clear desk edge behind the mounting point, and the arms reach forward roughly 25 inches at full extension, so allow room for the screens.