On holy days of obligation, the faithful are required to attend Mass.

The Code of Canon Law of the Catholic Church says that there are nine holy days of obligation other than Sundays, but it also says that the local conference of bishops may suppress some of them or transfer them to a Sunday. {https://www.omvusa.org/blog/catholic-holy-days-of-obligation/ }

On December 13, 1991 the members of the National Conference of Catholic Bishops of the United States of America made the following general decree concerning holy days of obligation for Latin Rite Catholics:

In addition to Sunday, the days to be observed as holy days of obligation in the Latin Rite dioceses of the United States of America, in conformity with canon 1246, are as follows:

January 1, the solemnity of Mary, Mother of God

Thursday of the Sixth Week of Easter, the solemnity of the Ascension*

August 15, the solemnity of the Assumption of the Blessed Virgin Mary

November 1, the solemnity of All Saints

December 8, the solemnity of the Immaculate Conception

December 25, the solemnity of the Nativity of Our Lord Jesus Christ (Christmas)

Whenever January 1, the solemnity of Mary, Mother of God, or August 15, the solemnity of the Assumption, or November 1, the solemnity of All Saints, falls on a Saturday or on a Monday, the precept to attend Mass is abrogated.

{https://www.usccb.org/beliefs-and-teachings/what-we-believe/canon-law/complementary-norms/canon-1246}

*In some dioceses the Solemnity of the Ascension is celebrated on the Seventh Sunday of Easter. {https://www.kofc.org/en/resources/cis/devotionals/holydays.pdf}