Hi eljei,
Can you please share some more information about the issue.
1.Just to confirm are you able to upload the file successfully? If yes then did you try to open it with the suggested URL after upload or its fails to load and throw an error as 404 not found?
2.Your SSL certificate is valid one for your localhost?
3.Your kentico media library folder having read/write permissions?
Note: As per the suggested information you getting on console it seems there is something wrong with HTTPS enabled and SSL certificate on your kentico site. To ensure can you check it with HTTP request example login to your kentico admin using HTTP http:/localhost/admin then try to upload the image and see what happen next?
Thanks
Happy to help !