In case anyone else needs a temporary workaround for a demo: Execute the following commands one by one (and ignore that they're different from what you would do in an actual git repository):

git checkout -b main
git branch -d master

Plus, if you have a remote:

git branch -m origin/master origin/main
git branch -d origin/master
mode remote
git checkout -b main
git branch -d master
mode local

Now all that's left to do is hide our hacky attempt to fix the original state. Fortunately, the command list is easy to find in the dev tools:

Issue is fixed in my fork and you can use it here.

Tagging @kuychaco , @gusshawstewart , can we get this fixed please? This feels really antiquated, now that the default is Main on most SCM systems.