Due to the architecture of Roon it is not possible to downgrade Roon versions. We have not received any other reports of USB DACs not working on MacOS with recent updates, and I can’t think of a change that would cause the behavior you are seeing directly.
I have two further troubleshooting diagnostics I would like you to perform that will give us insight into what is occurring here.
Try playing to the “System Output” zone in Settings > Audio while the Vega is selected as your MacOS audio device. This is the mechanism by which Spotify and other applications on the Mac are playing to the DAC.
Try playing to the Vega DAC using the Tidal application with “Exclusive Mode” enabled. This is how Roon is playing to the DAC. In the Tidal application on Mac, enter the audio settings (you can click the HiFi logo next to the volume control), select the Vega in the dropdown menu, click “More Settings” and then enable Exclusive Mode.
Starting with a fresh database may help resolve some of the performance issues we are seeing in your logs. To do this, make sure your Roon Database has been recently backed up, then use the following steps.
A. Open Finder and click Go in the top bar
B. Hold down the Alt key to unhide the Library folder
C. Click the Library folder
D. Rename the “Roon” folder to “Roon_old”
E. Rename the "RAATServer folder to “RAATServer_old”
F. Open the Roon application as normal. It will ask you to log in as if this were a new installation.
G. Only add a small amount of local content for testing purposes. If you have a Tidal account, local content won’t be necessary. Do not add any networked storage device.
H. Once Roon has opened to the overview screen, go to Settings > Audio and only enable the Vega DAC zone.
After you have performed this test, you may close Roon and return to your previous database instance. To do this, go back to the library folder, and name the current “Roon” folder to “Roon_test”. You shouldn’t have to modify the RAATServer folder again.