This Add to Calendar tool displays links to add events to various calendar types from information supplied by a calendar asset.
Example: https://www.unimelb.edu.au/dates/add2cal?id=3130435
This tool does not compensate for Time Zones or Daylight Savings.
The time displayed is 'floating' and defaults to that of the server - Australia/Melbourne, but the event will be added to your calendar in whatever your default time zone is.
Floating time is good for something like "Morning tea", which takes place at the same local time wherever you are.
Adding the extra variable tzid=UTC to your url sets the event to UTC (+0) time and takes no account of location/time zones, or daylight savings.
Specifying UTC is best for an event that takes place at a specific time regardless of where you are in the world, or what time zone your personal calendar is set to - eg: a meeting, or a webinar.