About url capitalization

assuming I have a page, lower cases url:
example.com/cat-cat1/
while if I enter capitalized C instead of lower case, like
example.com/Cat-cat1/
it will turn to 404.

And when I site example.com/Cat-cat1/ at google, it still shows 1 result, pointing to the original url: example.com/cat-cat1/

Should this situation draw my attention? Could I avoid the 404 from entering upper case url?

Yes, you can avoid it.
Depending on your server, there are different solutions. Either consult with an IT or provide your web server's type.

The http protocol is case sensitive, meaning that (depending on implementation) your server takes lowercased words and uppercase words as different and thus that is why you're getting the error.

Google stores the url as is, but google search is case insensitive. As long as you don't have urls explicitly ponying to a page with different case, then there's no problem at all.