Have spent ages last day or two trying to figure this out and still struggling!
Although Squeezebox support is enabled in Setup, Roon still not detecting WiiM Pro Plus as a Squeezebox device (does see AirPlay and Chromecast); therefore, I can’t enable Squeezebox-WiiM device.
Of note, the Roon and WiiM firmwares are both latest. Also, have disabled PC firewall in case it was a port issue but that didn’t fix.
Interestingly, I tried installing LMS and that found WiiM device immediately and I could play audio.
I did find a previous thread with similar issue but solution doesn’t apply to WiiM:
https://community.roonlabs.com/t/roon-cant-find-squeezebox-devices/124331/8
Any more ideas, please?