In Home Routines you first create a routine, then schedule it afterwards, rather than selecting a calendar day or month to place it on like a calendar event.
Just create a new routine (e.g., “Holiday tasks”) then open it.
At the very bottom of your task list, below the regular scheduling stuff, there is a sort of doughnut icon which says “Show in every month”. Just touch that row, and you will be able to select a set of months for the routine to be displayed.
This works in conjunction with any other routine schedule; for example, you can have a bi-weekly routine which is only shown in January and February.
If you schedule a routine reminder, it will be active on every day the routine is shown.
On the Home screen, you can use the All/Today button in the top left corner to toggle between the list of routines you have scheduled for today, and a list of all your routines.