You need to use the "Switch" capability instead of the "Dimmer" capability to get that.
More generally, RM picks the "flagship" attribute (or only attribute in the case of dimmers: level) when you choose a capability in the UI. Pretty much all dimmers also support on/off and therefore implement the Switch capability as well.
How do you think I should handle it then? (BTW, all your suggestions have been greatly appreciated)
If it's otherwise what you want, then the exact same--except one step before where you are in your screenshot above, choose the switch capability instead of dimmer (and use switch instead of level, which this will do).
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