You are not speaking to Apple here, but to other Apple users.
If you want to provide feedback to Apple, you could try contacting them at
Product Feedback - Apple
P.S.
Note that the Mac filesystems that most people use every day are case-preserving but not case-sensitive. That is, to, say, cat.jpg, cat.Jpg, and cat.JPG are treated as references to the same file. You'd have to deliberately reformat the drive as case-sensitive to make those different files (as they might be on other, more traditional, Unix systems).
If you are seeing some issue where you cannot select cat.JPG to upload it to the Web, it might be an issue not with macOS, but with the Web site.