USB directly off the RPi is generally described as ‘noisy’, so most people looking for better sound quality use one of the HAT boards.
Two popular HAT boards that provide a digital signal to a DAC: the Hifiberry Digi+ and the Allo DigiOne. Both have digital coax connections and the Digi+ also has an optical connection. Neither has USB.
Popular software choices are either Ropieee or DietPi. Both allow you to easily use the RPi/HAT as a Roon endpoint, controlled by your phone/tablet/laptop.
Personally, I have several RPi endpoints, all running Ropieee. I have not used DietPi, so can’t comment on the differences. Ropieee has been very easy to install and very stable.
We have two of these endpoints feeding DAC’s, one is a DigiOne, and one a Digi+. Both work well, but I would give a slight advantage to the DigiOne from a sound perspective.
I would second Sean’s suggestion. The Sparky is well made and the USBridge HAT is specifically designed for USB DAC connection. It would be a great place to start because it would be a complete solution.