I just like to have a clean ibuffer :)

After done with magit I want all magit buffers killed so that I can have a clean buffer list.

This configuration only buries the magit buffer which may or may not be what you want, I prefer to actually kill the buffer so this is what I use instead:

(use-package magit
    :preface (defun my/magit-kill-buffers ()
                 "Restore window configuration and kill all Magit buffers."
                 (interactive)
                 (let ((buffers (magit-mode-get-buffers)))
                     (magit-restore-window-configuration)
                     (mapc #'kill-buffer buffers)))
    :bind (:map magit-status-mode-map
                ("q" . #'my/magit-kill-buffers)
                ("C-x k" . #'my/magit-kill-buffers))
    :custom ((magit-display-buffer-function 'magit-display-buffer-same-window-except-diff-v1)
             (git-commit-summary-max-length 50)
             (magit-diff-refine-hunk t) ; show granular diffs in selected hunk.
             (magit-save-repository-buffers nil)
             (magit-define-global-key-bindings nil)))