I hopped on a meeting with myself for further testing.

1. I joined a Google Meet.
2. I speak and see that microphone is unmuted.
3. I mute in the Google Meet app, which works properly.
4. I lock the phone and iOS reports my microphone is not muted. However, the microphone is still muted.
5. I mute the microphone from the lock screen and I remain muted.
6. I unmute the microphone from the lock screen and Google Meet unmutes.
7. I mute the microphone from the lock screen and Google Meet mutes.
8. I unmute in Google Meet and the iOS lock screen unmutes.
9. I mute Google Meet but do not mute from the lock screen, and I try to use the microphone in another app, but am unable to do so.

Thus, my perception is that there is unexpected and/or inconsistent behavior here, because the initial Google Meet mute status does not propagate to the iOS lock screen. There does not seem to be an advantage to muting from Google Meet instead of the lock screen because the microphone is unavailable in other apps anyway.