I'm specifically thinking of git-flow (https://nvie.com/posts/a-successful-git-branching-model/); every build system I've interacted with has been some flavor of this. The crux here is that there is a single branch that deploys occur from. Not uncommonly, this is the default branch.
But with every build system I work with (which are: Jenkins, Concourse, Github Actions, and Gitlab CI) you can make any branch you want the branch-to-build-on.
I don't mean to say that it's not totally fixable. Up until this change, it was a reasonable assumption for any org to make, that the default branch will be the same for all projects. Now, either the default branch on any new repo must be manually set to the old default, or the build system must be updated to handle non homogenous default branches.
