I'm attaching an appointment I sent my gmail address just now and the resulting org entry (in the tmp.org file) that the [Export to Org] button produced using the gnus-icalendar-sync-event-to-org callback.

Looking at the text property gnus-data for the button, I see:

#s(gnus-icalendar-event-request "mah@nichework.com"
                                "appointment every weekday, start jul 24, 2020, end aug 24, 2020"
                                "The following is a new meeting request:\n\nSubject: appointment every weekday, start jul 24, 2020, end aug 24, 2020 \nOrganizer: \"Mark A. Hershberger\" <mah@nichework.com> \n\nTime: 9:00:00 AM - 9:30:00 AM GMT -05:00 US/Canada Eastern\n Recurrence : Every weekday.   End by Aug 24, 2020.   Effective Jul 24, 2020\n\nInvitees: hexmode@gmail.com \n\n\n*~*~*~*~*~*~*~*~*~*\n\ntest \n" nil
                                (24346 56144)
                                (24346 57944)
                                "FREQ=DAILY;UNTIL=20200825T035959Z;INTERVAL=1;BYDAY=MO,TU,WE,TH,FR" "903a5415-9067-4f63-b499-1b6205f49c88" "REQUEST" t required
                                ("Mark Hershberger")
                                nil)


----- On Jul 19, 2020, at 9:58 AM, Lars Ingebrigtsen larsi@gnus.org wrote:

> "Mark A. Hershberger" <mah@everybody.org> writes:
> 
>>>From skimming gnus-icalendar.el and icalendar.el, it looks like the
>> "BYDAY" parsing in icalendar.el only looks for one day, instead of the
>> multiples given.  I think gnus-icalendar.el's export to org functions
>> are only set up to insert one day instead of the multiple times required
>> by this rule.
> 
> Do you have a ical example file that illustrates the problem?
> 
> --
> (domestic pets only, the antidote for overdose, milk.)
>    bloggy blog: http://lars.ingebrigtsen.no