As for Vince Guaraldi and Peanuts, sure not all the songs from the show or album are religious but A Charlie Brown Christmas, aside from the songs Skating and Linus and Lucy and Für Elise, they were all Christmas songs. As for A Charlie Brown Christmas ..
A Charlie Brown Christmas - True Meaning
And FWIW - Feliz Navidad means "Merry Christmas, a prosperous year and happiness", the Spanish version and not all that different from We Wish You a Merry Christmas
Charlie Brown Christmas is an outstanding example of greatness emanating from defense of principle. The network et al thought Linus' speech (and a few other things) would kill the show. In reality, it made Charlie Brown Christmas on of the greatest "secular" Christmas specials ever.
I also love Rudolph, Elf, and a few other non-religious specials. However, you'll notice that Buddy, even though he and Jolie get together ultimately, wasn't trying to "hit it."
The left's disdain for BICO has noting to do with my disdain for that song. This is opportunistic woke-y-ness. There are oodles of songs about seduction, and to be sure the lyrics are more caustic ("It's So Easy" comes to mind). However, that GnR favorite isn't on my Christmas playlist, and I don't see Kelly Clarkson and John Legend railing against and remaking those lyrics.