Is it possible to add a key binding
helm-mini which would open the selected buffer in a new frame instead of in the current window?
This should already be available as
helm-buffer-switch-other-frame, bound to
C-c C-o. You can see available actions by hitting
TAB while in a Helm buffer.
helm-buffer-switch-other-frame, add the binding to
(define-key helm-buffer-map (kbd "M-RET") #'helm-buffer-switch-other-frame)