Heh. We have a Nest Mini at home that someone gave us, that we use as a smart speaker. Before setting it up, I popped it open and physically scraped out the MEMS microphones. Now that's a hardware mute.
Using voice commands to control music has always seemed like a sisyphean task to me. You're using a control method that directly conflicts with the state you'll generally use it in and song/artist names are so dense and confused that oftentimes you'll need multiple commands to hone in on what you actually want.
My "smart speaker" (aka desktop computer with massive speakers) is simply controlled by spotify sync which is absolutely not amazing but it's also not not terrible and far easier to control than times I've tried shouting at voice devices in the past.
The mic in these home devices is, imo, 90% for cooking and 7%[1] for other alarms and timers - they're relatively poor music platforms and only moved into the space because of how subsidized they were by Amazon and other companies.
1. (edit) bumped down from 9% to 7% because smart lights and thermostats are also quite prevalent.
I am curious. Are you sure you got them all?
But can you safely do this with multi room devices?