ENDOFYEAR Returns the last date of the year in the current context for the specified column of dates.
Syntax
ENDOFYEAR(dates [,year_end_date])
Parameters
Dates – A column that contains dates.
Year_end_date (optional) – A literal string with a date that defines the year-end date. The default is December 31.
Return Value
A table containing a single column and single row with a date value.
Reference Data
https://docs.microsoft.com/en-us/dax/dax-function-reference