mu4e has experimental support for the “transient” menus, as per
See (transient)Top. Because “transient” is not automatically available in
all Emacs version that mu4e support, you need to manually enable it:
(when (require 'mu4e-transient nil 'noerror) (global-set-key (kbd "C-c m") mu #'mu4e-transient-menu))