One plausible explanation I found is that there might be crystals flowing in the display, which makes sense because if you put it in your backpack sideways, the orange discoloration will be on the side that was looking down.
Is this a common issue? I have worked in laptop repair on and off as a certified tech for many brands since starting in 1998 (!) and have never once heard of crystal migration due to the orientation of a device. Very curious if you are hearing about this phenomenon outside of the thread you linked... thanks for sharing the info.
...I bought in October 2018... Am I looking at a screen replacement to get it fixed?...
Yes, I believe that will be the only fix. This appears to be a hardware issue - could be in the screen, a controller, or cable. My concern with spending any $ on this fix is that Apple laptops of this era have some longevity issues, so fixing this might just result in another problem in a year or two.
I am guessing you didn't get AppleCare, which means unless you luck out at the Genius Bar you'll likely be offered the same repair options (too expensive). Apple doesn't often make exceptions anymore, and Genius Bar techs don't have the same lee-way they once did to make courtesy replacements. Does your country offer extended protection for expensive equipment?
If I were in your shoes, I would sell this on the used market - some people won't mind this issue. You can then buy a new replacement - with AppleCare this time around. Are you interested in a different model? If you're willing to give up the Touch Bar, I would suggest giving a look at the 2019 Airs if you travel and move the laptop a lot. I am guessing from your bookmarks in the screenshot that the portability factor of the Air might be a nice feature. I have personally used the 2019 Air, 2019 13" base, and 2018 top line 15.4" and outside of very heavy lifting they all felt about the same speed (the top end models were faster on long-term heavy processing like extended computation for a rendering, encoding, or compiling task). When you first set up the machines an migrate your data, the Air might take 2x as long to do indexing, especially in Mail, but once it does the initial setup the speeds will be more in line with each other.
Whatever you do, I highly suggest considering AppleCare a part of the price of owning an Apple Laptop until things change in the future. Perhaps the 16" is the beginning of this change, but I think more likely reliability issues are a tradeoff we will continue to see for some time with Apple portables, as there have been reliability issues with almost every generation since they switched to Intel 20 years ago. (And even before that the consumer line of laptops was fairly problematic.)
