MoreKoo
Wohoo!
Clean install did the trick (as instructed in Cakewalk knowledge base).
 
I should have tried it in the first place. There must have been some Windows update in the background, or something, that broke Sonar configuration. All good now :)

Mind you, there are many people who have installed the latest Windows 10 security updates (sans drivers) who have never had issues with Sonar starting.

What you might want to do is prevent Microsoft from touching any hardware drivers.  For these, install them manually by downloading them from the respective manufacturer's websites.

Microsoft has this nasty habit of installing a generic driver rather than the most appropriate driver.

A free program called O&O Shutup can configure this for you.

https://www.oo-software.com/en/shutup10