> Please provide mode details about what you tried.  

OK, I will try.  I start emacs with 

    emacs -Q -l emacs_init/minimal-org.el

Here, minimal-org.el has the following contents:

    ;; Activate debugging.
    (setq debug-on-error t
      debug-on-signal nil
      debug-on-quit nil
      icalendar-export-sexp-enumeration-days 400)

    ;; Add latest Org mode to load path.
    (custom-set-variables
     '(package-selected-packages
       '(org-plus-contrib)))

In this setup, `M-x version` and `M-x org-version` bring up the following information:

    GNU Emacs 28.2 (build 2, x86_64-pc-linux-gnu, GTK+ Version 3.24.20, cairo version 1.16.0) of 2023-06-23

    Org mode version 9.5.5 (release_9.5.5 @ /snap/emacs/current/usr/share/emacs/28.2/lisp/org/)

`org-time-stamp` gives `<2023-07-24 Mo>`.

I create a minimal org-file `test.org` with the following contents:

    * Test 1  
    %%(org-anniversary 2022 07 23) Test1  
    * Test 2  
    %%(org-anniversary 2022 07 25) Test2 %d

I open this file in emacs and hit `C-c C-e c f` to export it to icalendar.  The file `test.ics` has the following contents:

    BEGIN:VCALENDAR
    VERSION:2.0
    X-WR-CALNAME:test
    PRODID:-//Marcus//Emacs with Org mode//EN
    X-WR-TIMEZONE:CEST
    X-WR-CALDESC:
    CALSCALE:GREGORIAN
    END:VCALENDAR