Resetting the Mac with Command+R may be a bit radical as a first step. Try this:
Several people reported a device discovery problem with Sequoia. Check macOS System Settings > Privacy & Security > Local Network, make sure Roon is allowed. If it is already enabled, toggle it off and on again. Then reboot the Mac. Seems to help most people.
Seems that the Sequoia update reset this for some people (not for me though).