Dear Mr @moderator
I love informative posts, sadly yours falls short on information
You'd best have a word with Hoover as a diode in series is how they added Low & High speed to vacuum cleaners. Obviously Hoover must be wrong and BS/EU Safety Standards wrong too
What's that? Oh, it's crickets
That's a direct drive induction motor, so mechanical schemes are out. To change the speed of induction motors, you really want to change the frequency, but that's not going to be cheap. You could change the applied voltage, like @pcar964's suggestion, but that's a) going to fvxk with the start capacitor and b) still a pain in the arrse.
Afaik diode is used to half the frequency, lower total implied DC voltage is a less important aspect