With the introduction of workspaces, we no longer support sub-projects in team workspaces.
Sub-projects are a handy way to organize projects in your personal workspace. But because project hierarchies aren’t synced across accounts (i.e., a shared sub-project in your sidebar could be a main project in someone else’s), we couldn’t make them make sense in a team workspace where everyone sees the same project list.
Early workspace beta testers have let us know that they need better ways to group and organize team projects, and it’s at the top of our list of things to work on next. If you have any suggestions or feedback, share it via this feedback form.