In the USA, was the Feast of the Immaculate Conception of the Blessed Virgin Mary a holy day of obligation or not?

My parish bulletin this Sunday listed Monday as a holy day of obligation, but then in the missal the entry for the mass said:

THE IMMACULATE CONCEPTION OF THE BLESSED VIRGIN MARY PATRONAL FEASTDAY OF THE UNITED STATES OF AMERICA - DECEMBER 9, 2024 - “This solemnity is not observed as a holy day of obligation in 2024, according to the USCCB'S liturgical calendar”

So…. Was is a day of obligation or not? I was happy to be there and it was a beautiful NO mass, our Monsignor sang the Eucharistic Prayer, and it was all very meaningful and pious, but was it an obligation for the parishioners?