org-agenda-export-to-ics by Alan M. Lafon (https://200ok.ch/posts/2022-02-13_integrating_org_mode_agenda_into_other_calendar_apps.html)

org-agenda-export-to-ics.el

;; To run export from Bash:
;; emacs -batch -l ~/.emacs.d/init.el -eval "(org-agenda-export-to-ics)" -kill
;; if [[ "$?" != 0 ]]; then
;;   notify-send -u critical "exporting org agenda failed"
;; fi

(setq org-directory "~/Dropbox/org/")
(defun set-org-agenda-files ()
  "Set different org-files to be used in `org-agenda`."
  (setq org-agenda-files (list (concat org-directory "things.org")
                               (concat org-directory "reference.org")
                               (concat org-directory "media.org")
                               (concat org-directory "shared_with/bob.org")
                               "~/src/your_company/admin/things.org"
                               "~/src/your_customer/admin/pm.org")))

;; Setting variables for the ics file path
(setq org-agenda-private-local-path "/tmp/dummy.ics")
(setq org-agenda-private-remote-path "/sshx:user@host:path/dummy.ics")

;; Define a custom command to save the org agenda to a file
(setq org-agenda-custom-commands
      `(("X" agenda "" nil ,(list org-agenda-private-local-path))))

(defun org-agenda-export-to-ics ()
  (set-org-agenda-files)
  ;; Run all custom agenda commands that have a file argument.
  (org-batch-store-agenda-views)

  ;; Org mode correctly exports TODO keywords as VTODO events in ICS.
  ;; However, some proprietary calendars do not really work with
  ;; standards (looking at you Google), so VTODO is ignored and only
  ;; VEVENT is read.
  (with-current-buffer (find-file-noselect org-agenda-private-local-path)
    (goto-char (point-min))
    (while (re-search-forward "VTODO" nil t)
      (replace-match "VEVENT"))
    (save-buffer))

  ;; Copy the ICS file to a remote server (Tramp paths work).
  (copy-file org-agenda-private-local-path org-agenda-private-remote-path t))