Hey there.
I can confirm that in this case, the main branch won’t be set correctly by default (coming back to the conversation here, it’s because the project isn’t bound).
And, even when a project is bound, should the default branch change… you’re stuck in this situation as well.
So for now, you have to either rename the main branch (and lose history / have a history that actually represents two branches).
I’ll move this to Suggest New Features so that it can get attention from the right folks, and maybe get some votes.