*taps microphone*
Is this thing on? Yeah the answer to what you can do about racism on Masto is chase racists off the platform. You literally don't even have to stalk them or anything, you just reply "fuck off racist" every time they pop up and if enough people do that the racists self-select away.
A lot of you folks KNOW this too, it's just awkward, and not personally rewarding for you, so you make up excuses for not doing it.
"What CAN white people do" - chase racists away. Very simple.