Example:
CASE WHEN YEAR("X"."y") >= 2019 THEN FILTER ROUND_DAY("X"."y") != ROUND_DAY("A"."b") OR ROUND_DAY("X"."y") != ROUND_DAY("M"."n")
OR ROUND_DAY("A"."b") != ROUND_DAY("M"."n") ELSE FILTER ROUND_DAY("A"."b") != 2019-01-01 OR ROUND_DAY("M"."n") != 2019-01-01 END
Neither CASE WHEN nor IF worked for me. I'm trying in a Component Filter, though a solution on a Sheet level could also solve my problem.