All cars are "designed to stand up to salt", including the cybertruck, just in different ways.
Most auto manufacturers use mild steels which are highly susceptible to rust, but mitigate rust by using various types of coatings. This has significant drawbacks because coatings can be compromised by wear, causing the underlying steel to fail to corrosion.
As my engineering professor always said, if you're willing to spend a few million dollars on a car, you can get one that will last a lifetime!
Yes, including the cybertruck. Tesla chose 301 stainless to mitigate rust. It is not a perfect choice. Neither are coatings on mild steel. All cars are designed to resist corrosion but can and will under the right (wrong?) circumstances. There is no perfect material that does everything. All have pros-and-cons.
It does happen with other cars. At my last job, the guy in the cubical next to me had a brand new car that had rust issues fixed under warranty. And traditional automakers don't warranty rust until the hole goes entirely through the body panel (i.e. rust perforation).
Remember, most traditional automakers are using steel with little to no corrosion resistance at all, and are relying on fragile coatings to do the work instead. This is not without its own drawbacks.
I think most body panels have been hot-dip galvanized electroplated then painted since the 80s instead of just exposed without even a clear coat. That should last at least 5-10 years even in the worst North American conditions before you see rust. Unless you imported yourself something low-end originally destined for India or China.
The car you linked to on reddit was a 2018 Grand Cherokee, which is ~7 years old now (5 years old when posted), so it would be expected -- and something you can just touch up. Note that in the comments they suggested it might even be covered under the new-vehicle limited warranty had it occurred in the first 3 years. Which makes sense, I'd consider that to be a material defect within that period of the NVLW.
Note that Tesla will sell you a cybertruck clear coat paint job for $5000. Probably a good investment.
Most auto manufacturers use mild steels which are highly susceptible to rust, but mitigate rust by using various types of coatings. This has significant drawbacks because coatings can be compromised by wear, causing the underlying steel to fail to corrosion.
As my engineering professor always said, if you're willing to spend a few million dollars on a car, you can get one that will last a lifetime!