Hi,
org-agenda-entry-text-cleanup-hook is not called when agenda is produced.
Org mode version 9.3.6 (release_9.3.6-471-g9e385d
Prove:
(defun ct-clean-agenda-entry ()
(message "XXX1"))
(add-hook 'org-agenda-entry-text-cleanup-hook 'ct-clean-agenda-entry)
But there is no output while agenda is displayed with a lot of entries.
I don't know why because in org-agenda-get-some-entry-text there is an unconditional
(run-hooks 'org-agenda-entry-text-cleanup-hook)