Custom DocType not editable

Hi,
I’m following the tutorial. At the step where it’s needed to create a second DocType named Library Member, it’s not possible to uncheck Custom? in Settings.
( I was able to do that at the previous step for the Article DocType, but not now)

This prevents me to create a controler because no folder has been created for the new DocType in the bench app directory.

I run in docker dev mode. I am logged in as an admin. Can’t find anything in the doc or the forum.

What am I missing?

Thank you!

enable developer mode and check it.

Thanks, yes I’m already in developer mode, with the yellow banner at the top