Lugano to Menaggio bus- Scary ride?

Very narrow? Not really, the road is two-lane throughout. Very high? Not at all. There is a 1-mile section just out of Lugano that you could describe as "high" above the lake - it's not that high - and 3 switchbacks in the descent to Menaggio. If that's a problem, then any travel in that part of the world will be a problem. The road is fully covered by Google Streetview, and since the Streetview cameras are on the roof of cars, they illustrate relatively well what the view from a bus window could be.

You can avoid a part by taking the boat to Porlezza and the bus from there. Slower, but you are on a holiday, after all...

I did it from my car and for me it was a nothing. If there was a hill or a switchback I don't remember them.

Nice breakfast at a filling station / bar part way. Didn't get fuel for the car, just us. Great coffee.

Thanks so much everyone, this is very helpful.