I went the "batshit insane" route and my microphone hole is plugged in with some clay.

It did most likely physically damage it forever, but at least I now know it's OFF for good.

i tried that with some sugru on an old phone (samsung s10e) and it does a really good job of blocking the microphone.

if you have a case on your phone its a lot less destructive too since you can just stuff the sugru into the microphone hole in the case. the case i was using was soft rubber so it was easy enough to pop out the corner of the case to be able to use the microphone for a call.

that wasnt my daily phone at the time though so im not sure how well it would work in reality. i could see myself forgetting to pop out the case when i get a call and the other person just handing up before i realised what was going on.

it also doesnt work on every phone. i tried the same thing on a pixel 5 but blocking the mic hole did nothing, but that phone uses an under screen speaker so maybe there is something similar going on with the mic

Why not shut it off in the bios?