TST, The Satanic Temple, the official name for the main organization of modern-day Satanism, has several holidays that it recognizes just like any other religion! Several of our holidays, whether in solemn remembrance or celebration, are inspired off of history's many holidays.
To start us off with the earliest holiday of the year, we have:

Lupercalia; February 15th
Lupercalia is a holiday based on the roman festival that went by the same name. Unlike the festival, however, Lupercalia only falls on the 15th. It's moreso a day of self-celebration and bodily autonomy. Not only is bodily autonomy one of our tenets, but this holiday is especially meaningful to me as a member of the lgbtq community.

On April 30th is Hexxenhacht
Hexxenhacht is a day of solemn remembrance and honor for those who were victims of superstition such as the witch trials. No one deserves to be imprisoned or attacked or killed over superstition.

On July 25th is Unveiling Day
Unveiling Day marks a milestone in TST when the keystone of this movement, the Baphomet with Children statue by Mark Porter, was unveiled in 2015 in Detroit! The statue was made with "'respect for diversity and religious minorities' in mind" and marks a new beginning of the Satanic Era. Unveiling Day is a celebration of religious plurality and the rejection of outdated religious dogma.

October 31st! Halloween!
I think it's cool that Halloween is an official holiday over here ToT
Being laced with religious dogma and often being called demonic or evil due to said dogma, we rather embrace it as a time to embrace darkness and face your fears with a costume and some candy!

Finally, we have Sol Invictus on December 25th
Sol Invictus is a celebration of freedom and separation from superstition. And promotes "...the pursuit and sharing of knowledge"! This holiday is especially important to me as it gives me an outlet to reflect on my derealization from the Protestant church that I was a member of in my youth and my newfound comfort in Satanism and science.
(and i do still celebrate christmas, just without the christian roots. it's a celebration of happiness and gift giving in my house <3)

It's important to say that not every modern-day Satanist acknowledges every one of these holidays! They're official holidays of TST, yes, but everyone practices them differently!

All of these descriptions are in my own words! To see the original descriptions of each holiday, go here: https://thesatanictemple.com/pages/holidays !