When uploading my screenshots, I got the message:
An error occurred: The theme screenshots must be maximum 3840x2160. The screenshot dark.webp exceeds this. Its dimensions are 4004x2024.
Perhaps this maximum could be mentioned in these docs?
Edit: also apparently it doesn’t care about the 16:9 aspect ratio
I just reduced my image to 3840 × 1941 and it’s working fine.