@HomeWifiPerson8 

I have a Deco BE68, and assume the iOS Deco app is the same?

It IS there, at least I can see it?

Select More to see this list, the QoS, and Enable it and you'll see this:

Select next after selecting Client Acceleration:

Set you ISP speeds, and the NEXT... and you get to select the device you want to allow the max. or limit to a value.

  @HomeWifiPerson8 "Lossless" is high fidelity sound, meaning less/no loss from analog to digital and back to analog signal to the speakers.  I have zero experience with Sonos, but to my understanding you'd want to have Lossless active for better quality music/audio?

If the cause of the issue is in fact poor WiFi then yes I would use QoS and set the Sonos as a high priority client.  This may involve enabling HomeShield for QoS function from the research I did on your BE63.