“Happy Holidays” is a kindness
My family celebrates Christmas. We’re all varying levels of religious, but Christmas is the holiday we celebrate together as a family. I don’t walk in the door December 24th and yell, “happy holidays!” I say “merry Christmas.” Likewise, when I talk to friends who celebrate other things, I call those out.
But if I don’t know you well enough to know what you do, I generally say “happy holidays.” I don’t operate a business, but if I did I would 100% say “happy holidays” as well since my customers would surely have a bunch of beliefs.
This is the way.