I would just replace the current values with just xhci. I've worked on the same model XPS and from what I remember it only had USB3 ports. I'll check the backup I have from that machine, maybe I backed up /etc/default/rtirq from that machine too.
Regarding the current values, snd is for prioritizing onboard stuff, usb doesn't do much anymore these days on more modern machines and if you'd like a keyboard or mouse without xruns you could opt for leaving i8042 in there.
Edit: here's the line from the backup I made from the XPS I owned:
So usb3 is in there, apparently my XPS was somewhat older than yours, I see you have a 9300 from 2020, mine was a 9360 from 2016. You could check with grep usb /proc/interrupts if you still have USB2 ports that load the ehci_hcd driver and add either ehci or usb to the RTIRQ_NAME_LIST variable.