There is a link to the Syncthing Code of Conduct at FAQ - Syncthing Community Forum, but it’s pointing at the master branch, which has been renamed to main.
GitHub handles this, by going to the default branch (main), and showing “Branch not found, redirected to default branch.” when it sees a branch that doesn’t exist, but I think it’s best to use a correct link, instead of relying on GitHub to handle the no-longer-existing branch.