Holidays

Nothing is known about culture-wide Mandalorian celebrations. The media offers a few glimpses as special occasions, however.

In Legends, we have this from the Star Insider #86 article "The Mandalorians: People and Culture" by Karen Traviss:

Settled races usually derive their annual festivals from the cycle of the seasons on their home world, but because the Mando’ade travel from world to world, they have often become disconnected from these cycles.  Those from Concord Dawn — traditionally a farming community — do still mark the end of the harvest by the world’s calendar, but generally the life-cycle events — birth, coming of age, marriage, death — have become the only ones celebrated.  The uncertainty of nomadic warrior existence means most Mandalorians celebrate life whenever they get the opportunity, enjoying ale, communal singing, and relaxing with their families and clan.

Traviss also created the idea of a regularly (often nightly) recitation of the names of friends and family who had died. This recitation starts with "ni su'cuyi, gar kyr'adyc, ni partayli, gar darasuum" (I still exist, you are deceased, I remember, you are eternal), followed by the names. In Order 66 (by Karen Traviss), some clones happen upon Kal Skirata and Walon Vau performing their yearly recitation of dead clones on the anniversary of Geonosis, but it was only those sergeants and whichever clones or other trainers were around at the right time and place. It was not a culture-wide activity.

In Disney canon, none of the shows (The Clone Wars, The Mandalorian, and The Book of Boba Fett) talk about any regular celebrations. In TCW, Duchess Satine Kryze has the city celebrate the arrival of Senator Padmé Amidala as an ambassador of the Republic. In TMS, the confirmation of a new member of The Tribe was a formal day of celebration that included banners and a special ceremony. All Mandos who were around and knew about it gathered for Grogu formally being made part of Din Djarin's family. There was a large gathering for the relighting of the Great Forge.

Of course, many fans have created their own ideas of what Mandalorians would celebrate in universe, and how they would do it. If you run across a holiday with a name or any details, you likely have found fan speculation and something that not every fan will know about or even agree with.