According to this page the vim editing mode can be enabled in the account settings, but I can not find it. Even after joining the beta program there is no option to enable this feature.
How can I enable the vim editor mode in Overleaf?
(I'm on support staff at Overleaf.) Sorry about the outdated blog post. Those instructions refer to our old v1 editor which has now been retired. I'll make a note to update the post with new instructions.
On Overleaf v2, this setting is managed in the project menu. Open a project, then click on the Overleaf menu in the upper left. Scroll down to "Keybindings" where you can select Vim or Emacs. This setting is remembered across projects.