I believe if you live in the rust belt, the 2018+ start off rusting where you won't readily see it.
When I bought my 2021 LT 1.5T AWD used in June 2024 w/ 34K miles on it, It had some pretty significant surface rust forming underneath the vehicle on the unibody, subframes, floor pans, rocker panel crimps and spot welds, etc.. Pay particular attention to the rocker crimps under the vehicle, as the rocker panels are completely clad in plastic, which hides everything. I live in the Buffalo NY area, as my Equinox has it's whole life.
I do my own fluid film and/or woolwax treatments and treated the vehicle right after I bought it. I'm still not confident on what's going on under the plastic rocker panel cladding and there's no good way to shoot oil/wax based treatment in there. I was just partially underneath my 2021 yesterday as I did an engine oil change. There are some areas I'd like to touch up with FF/WW before this winter, which brings me to another good point. Oil/wax based treatments need to be reapplied every year or every other for bad winter climate areas. These are not once and done deals.