The problem you are describing is solved by saving/persisting times in UTC. The calendar will display the event by using the user's current timezone and the UTC time to determine local time.

You can store times in UTC if you want, but that alone doesn't solve the problem. A UTC timestamp alone is not enough information about an event.

Consider a Doctor's appointment for Dec 20, 2026 2pm in Calgary. Regardless of whether its booked a year ahead (ie before the new time zone rules were decided) or a week ahead (after the rules were decided, and consequently a different UTC time), the expectation is that it will be at at 2pm local time.

Generally speaking, UTC + localization works for past events, but not future ones (see sibling comments)

But doing that breaks the opposite (and more common) problem: all the meetings in Alberta, planned before the change to the time zone was announced, will have the wrong hour.