From the USCCB web site:
In the Catholic Church, all Sundays and certain other feasts during the year are described in church law, as well as in common language, as holy days of obligation, meaning that Catholics are obliged by law to assemble together to worship God on those days. They ordinarily do this by participating at Mass. In the dioceses of the United States, there are six holy days of obligation:
January 1 – Mary, Mother of God
May 21, 2023 – The Ascension of the Lord (40 days after Easter; transferred to Sunday in many dioceses, including the Diocese of Palm Beach)
August 15 -The Assumption of Mary
November 1 – All Saints’ Day
December 8 – The Immaculate Conception of Mary
December 25 – Christmas
Holy days of obligation other than Sundays are always ranked as solemnities and will replace seasonal Sunday Masses when they occur on a Sunday, except the Immaculate Conception, which always falls in Advent.