This is a them issue, not a you issue. To put it in context, your neurodivergent conditions cause you to not be able to join in and the world not to be accessible for you.
If they had someone who was a wheelchair user, they would not just leave them outside with no ramp and just say it is a shame they can't join in.
If they had someone who was blind/low vision, they wouldn't just tell them to get on with it when navigating an unfamiliar space.
When it comes to ND conditions, people can't comprehend how disabling it can be at times and the statement just get on with it/over it or the exclusion that comes from, in this case, loud music being played, is ableist and ignorant.
This is not your fault, you have not ruined or broken anything. They are not being inclusive and are not making Christmas accessible.
P.S. I am ND and have spent years trying to get my head in a better place from thoughts like you are having.