There was one review that compared the mics between the 2018 and 2020 and it sounded pretty much the same, which is to say it was way worse than a dedicated mic.
I can’t remember if it was the MacRumors review or if it was Rene Ritchie’s.
EDI
Not Rene Ritchie’s but it does test it.
Rene Ritchie 10:29:
It’s in the MacRumours hands on at 2:14: