What Git really needs, is some kind of "branch alias" feature. Some config setting like "branch_alias.main=master", and then I could always write "git checkout main", and it would checkout "main" if that exists, and "master" if it didn't (and vice versa). That would solve it in most cases – except for the rarer "we decided to use neither main nor master" and "we made a new main branch but kept an outdated master branch hanging around".
I think that it is probably not necessary or helpful to rename branches in existing repositories, but you can do that if it is helpful for what you are doing.
If you upload a repository to GitHub, you can use whatever default branch name it already has with no problem. I know because I did upload one that uses "trunk" as the default branch name, and it did not cause any problem. (I used "trunk" as the default branch name because it is a mirror of a fossil repository which uses "trunk" as the default branch name.)
(And, someone does get a minor benefit to call it "main"; it is two letters shorter than "master". Of course, that is minor, but it isn't quite nothing.)
But it's simply less risky and less work to just call it "main".
It doesn't matter, and nobody gains anything from calling it "main" -- but if we call it "master" someone might get offended or waste my time arguing over it.
There is no incentive to insist calling it "master". So similarly, I guess we'll end up calling you "photonically disadvantaged" :)
Or maybe we can give it a positive spin and call it "darkness unimpaired"? (Just kidding of course)