What I see here seems like Americans(Californians?) trying to force their cultural preferences on the rest of the world. And they think they're doing good?
They don't own the English language.
For me, it's a somewhat archaic term for "teacher", especially for something like fencing (https://sirwilliamhope.org/Library/Hope/ScotsFencingMaster/) or dancing (https://playforddances.com/). At my school, if you had forgotten to bring your prep (homework) to a lesson then a trip to the masters' common room at break time to hand it in would be necessary (it was a very traditional school, and this was a few decades ago).
There's been controversy about the word in other communities with which I've been involved over the past couple of decades, though again not related to slavery. In this case it's considered rude and or arrogant to refer to yourself as a "master" if teaching certain skills, as the word has connotations of considerable expertise and is not so widely known any more as meaning that one teaches. So, a "fencing master" would be interpreted not as a teacher but as one of the world's greatest sword fighters.
Now, asking with all curiosity: do people actually feel excluded over this sort of language? If so, what’s your story?