filtering events in ICS calendar

Re [iCal CALENDARURL.ics?category=bananas] . It could if the application serving up the url would then return only the events in that category (nothing to do with this plugin)

Alternatively try
https://icalevents.com/support/documentation/shortcodes/#parameters

Ok, so if I understand correctly, you’re saying that the browser request:

https://MYPAGEURL?category=bananas for the calendar displayed by the shortcode [iCal CALENDARURL.ics]

is actually a different sort of request from using the shortcode on a page:

[iCal CALENDARURL.ics?category=bananas]

I had thought they should function the same.

They are related but different.

CALENDARURL.ics?category=bananas will only work IF the application CALENDARURL supports that kind of event selection as per the specification https://icalendar.org/iCalendar-RFC-5545/3-8-1-2-categories.html.

Some applications just don’t offer CATEGORIES.

https://MYPAGEURL?category=bananas where https://MYPAGEURL is a wordpress website running amr-events plugin and has events created as custom post types should work to serve up just those custom post type events with that category, similar to this where taxonomy sport is used https://test.icalevents.com/agenda/html5-agenda/?sport=random. However it won’t work to filter categories from the ics feed, only for events created in wordpress (it uses the wp query). See https://icalevents.com/5261-categories-from-ics-files/