No matter in which mode I am currently in, is there a general way / key combination to open the help file related to the currently active mode?
M-x describe-mode, which is bound to
C-h m by default. It shows the current major mode, as well as all current minor modes.
If you want to jump directly to the description of your current major mode, then either evaluate
(describe-function major-mode) (via
M-:) or bind it to a key, for example:
(defun my/describe-current-major-mode () "Describe the current major mode via `describe-function'" (interactive) (describe-function major-mode)) (global-set-key (kbd "<f5>") #'my/describe-current-major-mode)