Using the Qobuz PC app (not Roon!) and search for “5.1” (or “multichannel” or “surround”).
They will play only as stereo in Qobuz.
However, if you flag them as favorites in Qobuz, they will also appear as favorites when you choose Qobuz favorites within Roon and, with suitable connected equipment, they will play in 5.1.
Don’t expect much but it does prove that multichannel is supported in principle!