GitHub made the move to rename the
master Branch to
main. The reason for this change is to get rid of any holdover references to slavery and replace them with terms of inclusion that cannot be misconstrued.
GitLab also has aspirations to change the default but however, these have not yet been implemented. The same goes for the Git project itself.
It is currently possible in both Platforms to configure the main branch name of a project and GitHub also allows to an organisation default.