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Hopefully your knob is passive attenuation
Yes, as described, just an Alps volume potentiometer in a box with phono sockets on the back. https://amzn.eu/d/2EnyQyf other colours and retail platforms are available
simple for me does mean a volume knob
There's no reason why you couldn't turn the volume to max on the remote/app/on-speaker control and use the knob-in-a-box as your user interface
Hopefully your knob is passive attenuation.
In fairness leaving the bluetooth aside the M20's not a bad option if you want everything in one box. My own experience of one box solutions at that price point is they fail and when they fail it's sudden and total.
I would add that simple for me does mean a volume knob not a remote.