I am sharing a bug report from emacs -q. I don't know how to use a different org-version that the built-in (or if I should).

Emacs  : GNU Emacs 29.2 (build 2, x86_64-w64-mingw32)
 of 2024-01-18
Package: Org mode version 9.6.15 (release_9.6.15 @ ./emacs-i686/share/emacs/29.2/lisp/org/)

current state:
==============
(setq
 org-link-elisp-confirm-function 'yes-or-no-p
 org-bibtex-headline-format-function #[257 "\300
\236A\207" [:title] 3 "\n\n(fn ENTRY)"]
 org-persist-after-read-hook '(org-element--cache-persist-after-read)
 org-export-before-parsing-hook '(org-attach-expand-links)
 org-cycle-tab-first-hook '(org-babel-hide-result-toggle-maybe org-babel-header-arg-expand)
 org-archive-hook '(org-attach-archive-delete-maybe)
 org-odt-format-inlinetask-function 'org-odt-format-inlinetask-default-function
 org-ascii-format-drawer-function #[771 "
\207" [] 4 "\n\n(fn NAME CONTENTS WIDTH)"]
 org-cycle-hook '(org-cycle-hide-archived-subtrees org-cycle-show-empty-lines
          org-cycle-optimize-window-after-visibility-change
          org-cycle-display-inline-images)
 org-export-with-broken-links 'mark
 org-export-with-clocks t
 org-persist-before-read-hook '(org-element--cache-persist-before-read)
 org-export-default-language "es"
 org-mode-hook '(#[0 "\300\301\302\303\304$\207"
           [add-hook change-major-mode-hook org-fold-show-all append local] 5]
         #[0 "\300\301\302\303\304$\207"
           [add-hook change-major-mode-hook org-babel-show-result-all append local] 5]
         org-babel-result-hide-spec org-babel-hide-all-hashes)
 org-export-headline-levels 888
 org-latex-format-drawer-function #[514 "\207" [] 3 "\n\n(fn _ CONTENTS)"]
 org-icalendar-use-scheduled '(event-if-not-todo event-if-todo-not-done)
 org-latex-format-headline-function 'org-latex-format-headline-default-function
 org-confirm-shell-link-function 'yes-or-no-p
 org-export-with-date nil
 org-html-format-drawer-function #[514 "\207" [] 3 "\n\n(fn NAME CONTENTS)"]
 outline-isearch-open-invisible-function 'outline-isearch-open-invisible
 org-export-with-todo-keywords nil
 org-icalendar-include-todo 'all
 org-export-initial-scope 'subtree
 org-odt-format-headline-function 'org-odt-format-headline-default-function
 org-export-with-statistics-cookies nil
 org-agenda-before-write-hook '(org-agenda-add-entry-text)
 org-export-with-author nil
 org-src-mode-hook '(org-src-babel-configure-edit-buffer org-src-mode-configure-edit-buffer)
 org-confirm-elisp-link-function 'yes-or-no-p
 org-export-with-timestamps nil
 org-speed-command-hook '(org-speed-command-activate org-babel-speed-command-activate)
 org-html-format-inlinetask-function 'org-html-format-inlinetask-default-function
 org-ascii-format-inlinetask-function 'org-ascii-format-inlinetask-default
 org-export-with-tags nil
 org-odt-format-drawer-function #[514 "\207" [] 3 "\n\n(fn NAME CONTENTS)"]
 org-persist-directory "c:/Users/KC/AppData/Local/Temp/org-persist-KWkfxv"
 org-icalendar-combined-name "icalendar-org-agenda"
 org-export-backends '(html icalendar latex odt)
 org-icalendar-combined-description "icalendar-org-agenda-files"
 org-fold-core-isearch-open-function 'org-fold--isearch-reveal
 org-latex-format-inlinetask-function 'org-latex-format-inlinetask-default-function
 org-persist-before-write-hook '(org-element--cache-persist-before-write)
 org-tab-first-hook '(org-babel-hide-result-toggle-maybe org-babel-header-arg-expand)
 org-link-shell-confirm-function 'yes-or-no-p
 org-babel-pre-tangle-hook '(save-buffer)
 org-agenda-loop-over-headlines-in-active-region nil
 org-occur-hook '(org-first-headline-recenter)
 org-export-with-drawers t
 org-metadown-hook '(org-babel-pop-to-session-maybe)
 org-link-parameters '(("attachment" :follow org-attach-follow :complete
            org-attach-complete-link)
               ("id" :follow org-id-open)
               ("eww" :follow org-eww-open :store org-eww-store-link)
               ("rmail" :follow org-rmail-open :store org-rmail-store-link)
               ("mhe" :follow org-mhe-open :store org-mhe-store-link)
               ("irc" :follow org-irc-visit :store org-irc-store-link :export
            org-irc-export)
               ("info" :follow org-info-open :export org-info-export :store
            org-info-store-link :insert-description
            org-info-description-as-command)
               ("gnus" :follow org-gnus-open :store org-gnus-store-link)
               ("docview" :follow org-docview-open :export org-docview-export :store
            org-docview-store-link)
               ("bibtex" :follow org-bibtex-open :store org-bibtex-store-link)
               ("bbdb" :follow org-bbdb-open :export org-bbdb-export :complete
            org-bbdb-complete-link :store org-bbdb-store-link)
               ("w3m" :store org-w3m-store-link)
               ("doi" :follow org-link-doi-open :export org-link-doi-export)
               ("file+sys") ("file+emacs") ("shell" :follow org-link--open-shell)
               ("news" :follow
            #[514 "\301\300\302Q\"\207" ["news" browse-url ":"] 6
              "\n\n(fn URL ARG)"]
            )
               ("mailto" :follow
            #[514 "\301\300\302Q\"\207" ["mailto" browse-url ":"] 6
              "\n\n(fn URL ARG)"]
            )
               ("https" :follow
            #[514 "\301\300\302Q\"\207" ["https" browse-url ":"] 6
              "\n\n(fn URL ARG)"]
            )
               ("http" :follow
            #[514 "\301\300\302Q\"\207" ["http" browse-url ":"] 6
              "\n\n(fn URL ARG)"]
            )
               ("ftp" :follow
            #[514 "\301\300\302Q\"\207" ["ftp" browse-url ":"] 6
              "\n\n(fn URL ARG)"]
            )
               ("help" :follow org-link--open-help :store org-link--store-help)
               ("file" :complete org-link-complete-file)
               ("elisp" :follow org-link--open-elisp))
 org-html-format-headline-function 'org-html-format-headline-default-function
 org-metaup-hook '(org-babel-load-in-session-maybe)
 org-icalendar-combined-agenda-file "~/2-Areas_R/NOTAS/org-mode-agenda.ics"
 org-icalendar-categories nil
 org-export-preserve-breaks t
 )

Ypo <ypuntot@gmail.com> writes:

If I were able to fulfill a good process to export from agenda to 
icalendar, maybe we could share an easy process, useful for a lot of 
users that miss a good android calendar visualization. Do you think it 
could be possible to export, in an async way, a calendar file every time 
when a new timestamp, Schedule or Deadline are added to a buffer? What 
would happen if an export process is already running and a new timestamp 
is added? Would it be robust enough or prone to errors? I can see that 
even if a footnote is not correct, the process seems to be interrupted.

You can just do it on timer or when the file changed.

Actual state: when I try to export to icalendar, the behavior is quite 
confusing:

+ [c] Combine all agenda files: I don't get any ics file. I don't know 
what is the problem.

+ [a] All agenda files: I get just an ics file. I thought I would get 
one file for each agenda file.

It would help if you provided an MWE. See https://orgmode.org/manual/Feedback.html#Feedback
It is extremely hard to diagnose things blindly.