After some thought I have installed the demo version of Syntorial. It offers the first 22 lessons (out of 199). I have started today with pulse and saw waves. So far so good.
The full version costs 131,99 €, a respectable investment. I wonder whether anyone here has tried it.
I’m also curious about other ways to learn about sound synthesis. I am not an enthusiast of structured learning, but having a job, family responsibilities and some passion for sport, the time left for “music” is limited and I welcome some structure. Otherwise time flies just browsing and poking through virtual instruments and presets.