FWIW I've been using Linux for USB audio since kernel version 3.2 up through 5.19, and a few of my systems are now on kernel version 6.0. I've never noticed any USB sound quality changes in any kernel versions, except in the case of one piece of hardware that was misbehaving prior to kernel 5.0 (i.e. that piece of equipment had loud obvious dropouts caused by buffer underruns, which stopped after 5.0).
They're always improving the kernel, but assuming the hardware is working correctly, I would be hesitant to expect any subtle changes in sound quality. If you're convinced you've spotted a change, it will be hard to narrow down what happened because every single minor kernel version has changes to the USB audio subsystem. Maybe step through the minor kernel versions and see if you can bisect the exact version at which the change occurred?