Hey Lars, hope all is well!
Good question. It definitely does depend on a site-by-site basis. Some sites may very well have one and publicly promote it on the site. Others, by contrast, may have them an not say anything at all about how to access it.
The Events Calendar adds an iCal address to a site uniformly so that it can be found at: [your-site]/events/ical. But that doesn’t mean other sites will employ it the same way.
Sorry I don’t have a concrete answer for you here, but I do hope this at least help clarify why it’s tough to tell.
Thanks,
Geoff