Sure it is.
Willfully denying what Jesus Christ has said to do and accepting instead what society and culture says to do is violation of the 1st command and possibly the second...especially with regards to idols such as the trapping of Christmas and Easter.
And that's not even considering the 4th commandment!
Now, other than for the UCG and maybe a couple of other sects, it’s not a sin at all. It’s not even considered in the subject of repenting, therefore.
Hellllooo! THAT'S the problem!!
Eze 22:26 Her priests have violated My law and profaned My holy things; they have not distinguished between the holy and unholy, nor have they made known the difference between the unclean and the clean; and they have hidden their eyes from My Sabbaths, so that I am profaned among them
That's traditional Christianity in a nutshell my friend....
You’ve bought into a secret decoder ring version of St. Paul, the Apostles, the Church.
It’s contrary to the plain reading, contrary to what Christians believed and taught from the Council of Jerusalem to the present day. It has no rational or factual basis; it relies on folks’ willingness to set aside the plain truth in favor of grand hidden conspiracies.
The same sort do this in other areas such as government, health, economics...