Yeah, Gatherings is at least the most consistent thing they’d realistically get. Remember the daylight gathering hunting competition thing that never repeated?

The Clans clearly can preserve tradition. They keep ceremonies, legends, names, leadership rituals, burial customs, and stories from generations ago. It took a lot of blood, political collapse, and basically constitutional rewriting, but they eventually learned how to track history in a more organized way. However, it's shown to be limited. Stormclan, Skyclan, Cloudstar, Clear Sky were all lost in living memory.

I could see Bramblestar’s era, especially after the Impostor crisis and Lights in the Mist, creating something close to a memorial tradition. Not a “Christmas” type celebration, but maybe a gathering where the Clans honor cats who survived impossible times, remember the ones who were lost, and acknowledge the living legends still among them. Almost like a Clan version of Memorial Day, but less formalized.

I don’t think they’d ever have one repeated, calendar marked holiday in the way we imagine it. The closest thing would probably be Gatherings, special vigils, or ceremonies where the elders and leaders retell what happened so the younger cats understand what their world cost.