There may be few real alternatives. But this is a choice: You're getting the information, you're making a choice to use all features, use limited features, or just drop the app.

And you have explicit control and granular control, even if 99% of the people won't ever use it. Before, if you didn't want Facebook accessing your Microphone, the only option was to not use the app at all. Now, I can specifically disable that option.

Facebook may just make the app not run unless you give it mic permission. Of course you don't have to run it. I have seen apps that explicitly refuse to run unless you give them the permissions they want on iOS even though they shouldn't need them for 99% of their functionality.

Wouldn't such a behaviour be against GDPR? Probably not because of technicalities, but then I would hope the EU to make yet another piece of legislation to address this.

That's where Google/Apple should step in and ban those apps from the store.

Of course it works, why wouldn't it? If you want a crippled device that never lets anything access to data, you can always buy a dumbphone.