The Calendar integration and related Trigger is an extremely poor solution to this problem. If you want to have multiple events in a single Calendar, the Trigger cannot handle that by itself, and you have to use a Template condition to check the data for the specific event, which is inconvenient at best.
Calendar triggers are inadequate for multiple events, Time triggers with datetime helpers do not support recurrence, and Template triggers are convoluted and inconvenient to deal with. And the Calendar and Time triggers both require pre-configuration outside the Automation setup itself, which is also inconvenient. These are woefully inadequate solutions to the OP’s use case.
There needs to be a simple trigger where you specify a date, with an optional recurrence period. That’s it. None of these user-unfriendly workaround ideas where you have to first create a Calendar, then create an event, then write out a template. Or first go create a datetime helper that doesn’t support recurrence.
Just put a Date picker and a recurrence dropdown into a trigger interface, or fix the Calendar trigger so it actually supports triggering on specific events instead of triggering on every event only.