I have the same issue! I've had the SB3 for about 10 months now. SB3 just released in may 2020 which was 7 months after surface laptop 3 release. For those of you who don't know. Surface laptop 3 has the same issue of randomly cracked screen(no drop) 3-4months after it's release. I don't use my laptop everyday so that may be why I am only experiencing this issue now instead of 4 months in like some of the others.
I have only taken this out of the house once like 3 months ago. The crack seemed to spontaneously appeared today. It was fine one moment and when I came back from the restroom I noticed the crack right away because I keep my taskbar at the top of the screen so it's easier to access tabs when I'm drawing or writing.
Sure it's a small crack on the top of the screen but for an expensive purchase I expect it to last for years especially if I didn't drop it or spilled anything on it. I wonder if Microsoft changed manufacturers or if they are purposely doing this since the Microsoft warrenty only lasts for 1 year and doesn't cover cracked screens unless you have physical warranty.
I draw/use the surface book for taking notes and you can definitely feel the crack on the screen when writing. Plus I'm also scared of the crack spreading.
As you can see in my third photo that there are no screen bleedings (screen bleeding or dark spots on the screen usually indicates a dropped laptop). The crack gross from the microphone dot to the right of the screen

