This is a strange one for me, as before the framework laptop I had my 7+ years MacBook Pro (2015) and never had anything similar.
Somehow, the bottom cover started to “fade” in the area where I keep my hand.
Did anyone have similar issues with the cover/trackpad?
Other than that, I love this laptop 
Hi,
Thanks for updating the title.
Unfortunately, I don’t think that’s the same as is quite smooth and I couldn’t clean it.
Also, that’s the only area, so is not where I keep my hand while typing.
The only other laptop I can compare with is my old MacBook, and I didn’t have anything similar on that one.
I believe the bottom cover on the 16" is painted magnesium, so it sounds like the paint may be wearing off in that spot.
That makes sense then.
A bit strange, as that’s the only spot and I haven’t used the laptop too much.
Almost all the newer MacBooks are a machined basically straight aluminum; no painting, coatings, etc. The primary function was the conduction of heat to keep the noise from fans to a minimum. Other benefits are:
That spot in your picture does look like paint worn away, or maybe it was anodized and reacted with something (skin oils, etc.) starting on the edge. 
