It's not cultural appropriation in the sense that you are commodifying or personally benefitting/helping yourself to sacred cultural artefacts or symbols.

If you aren't wearing one to pass yourself off as if you are Arabic when you're not then that's one thing off the list.

If you aren't selling keffiyeh produced in China at a stall at some hippy market that's another thing off the list.

Keffiyeh aren't sacred, so that's another thing off the list.

Think of it like a sombrero. Not a tacky prop sombrero but an actual sombrero. If you lived in a desert climate or you were travelling through a desert area and you bought yourself a sombrero from a Mexican milliner to wear, that's not cultural appropriation it's just a wise choice and a Mexican is going to look at you wearing your sombrero and they're either going to think "That's a nice sombrero - I wonder where they bought that" or "Finally, a güero has enough sense to wear a wide-brimmed hat under this beating sun. Usually they only come wearing a baseball cap at the very most."

I wear a keffiyeh often, as a white person, and the only time I've ever had people notice it is when a person of Palestinian heritage in a professional capacity felt comfortable enough to open up to me about their political opinions about Zionism and the abuses that Israel is inflicting upon Palestinians (which was ballsy given the context and the fact that there could easily have been repercussions for their employment) and another person who was a migrant from an Arab country who was gushing over the colour of mine and who ended up being an instant friend because I was wearing it.

Think about how you feel when you see someone in the wild wearing a hamsick or antifascist symbol. That's probably a decent approximation of how a Palestinian would see an outsider who wears a keffiyeh.