I still don't know if any of you are still interested. But there are some good developments. About Rouvy, I decided the main reason I didn't get a decent technical answer from them is that their native language is probably Czech. I did receive a follow-up response, not terribly enlightening but at least it showed more interest. I may still consider their app.

My sweetie, which is to say my wife of 41 years, has been enjoying riding Zwift, finding the course details and other riders to be quite a motivator. But she really wanted to see her cadence along with power. So I decided the problem with reading the Yahoo cadence sensor is that Bluetooth is a limiting factor. So I ordered a not-terribly expensive ANT+ dongle with 3ft USB extension cable from some online seller. (I suppose ANT+ dongle could be pronounced ANT 'nd'uncle seein' as how it does have the "and" between the ANT and the "d'ungle".) Anyway, we rode it today, works like a charm. Zwift identifies the cadence sensor as either Bluetooth or ANT+, so I connected to the ANT+ entry and lo! both speed and cadence showed up. 'Zactly like it was supposed to.

My sweetie just upper her FTP after pedaling at 90rpm for 45 minutes!