To answer your question regarding ‘[%BeginOfCurrentYear%]’] and why it also includes requests on the 1st of january - This datetime is the actual beginning of the year, 01-01-YEAR 00:00:00. This means that any leave that is requested starting later than 00:00:00 will be included in the retrieve.
My appologies. I've already solved the question myself. By using the year-from-dateTime function, I can achieve the goal of the assignment more effectively. The end result is: [Status='Approved' and year-from-dateTime(StartDate) = year-from-dateTime('[%BeginOfCurrentYear%]')]
I will open a ticket in the course and ask them to correct the lecture.