FYI, Kbin lets you block entire domains natively, though in a roundabout way.
Looks like you're using kbin.social, so you would put https://kbin.social/d/domain_you_want_to_block in your address bar, which brings up that entire instance (including lemmy instances) as a magazine. Then just block in on the right, the same way you would block a community/magazine.
You can check which domains you've blocked in your settings. Go to Settings > Blocked > Domains.
I think what you're trying to say is that the lack of racial diversity is unfortunate, but people are reading it as "unfortunate we have all these white people."
Probably just change the wording to that effect, or maybe something about how having such a large majority of a community from a single race can cause people from other races/ethnicities to feel left out, etc.