Can’t find additional holiday calendar option

Hehehe71 wrote:

I don’t see the option to add holiday calendar from other places.

That's because the Calendar app provides only one holiday calendar and this is based, I am presuming, on the location you have set as part of your Apple ID and to which your device is signed in. Even that is problematic in geographically large countries with lots of different regions or jurisdictions, each with their own set of holidays in addition to a national list.

My state in Australia has unique days off not included in a national list, just as the other states do, and I'm not interested in having their holidays in my calendar. If I wished to have a subscribed calendar I would install this one provided by my state government, but a long time ago I set this up myself in a new calendar in the Calendar app. You will also note on that page the list of school term dates which would be useful for parents of school-age children - but only here in Victoria; the other states have different dates. So you can see how I find that a set of dates to be effective needs to be local rather than national.

If you want to subscribe to holiday calendars of other regions I have seen this site which is a good source.