Hello @amandomino,
I have been reviewing code to see how including the define I mentioned may have failed. I think perhaps it could have been caused by how it was copied from this forum then pasted into your wp-config.php file. This reply I am wrapping the code with a code tag in hopes it copies better and using double quotes.
Please copy the following line and add it near the top of your wp-config.php which is found in the root folder of your WordPress website.
define("POWERPRESS_DEFAULT_MEDIA_URL", true);
IF you have any caching plugins or caching services tied to your web hosting, please clear then.
Once you have the define in place the following setting should appear: https://create.blubrry.com/wp-content/uploads/2017/02/default_media_url.png
Thanks,
Angelo