Yes, I have, but it doesn't make any difference.
Interestingly, I can successfully subscribe to the calendar (an Office 365 calendar) on MacOS Catalina, adding it to iCloud so that I can then also see it and all the details it contains if I log into iCloud Calendar online, so the problem seems to be the final step of getting iOS 13.6 on my iPad and iPhone to load the events: the iOS Calendars show the new calendar under iCloud calendars (I put it there to be sure it syncs across all devices) but the events in that calendar don't show even though the calendar is ticked in the list of calendars.