Interesting. I wonder if maybe the smaller models (Air, 13" and maybe 14" Pro) are more prone to this? I've had very little trouble with it on 15" models from 2015 onward or with the 16" M1 Pro.
I got the marks all the time on my 2016 13" MacBook Pro, too. I even had the keyboard (and by extension battery) replaced in that machine, and Apple "professionally cleaned" the screen. There were still some permanent keyboard marks on the screen after the cleaning. It's not just oil, but permanent abrasion marks after a while.
