If you upload a file via FTP, this file will not be found by your WordPress media library at first. Generally speaking, the WordPress Core does not support this. WordPress is designed to work with an abstract implementation of a virtual file system, e.g. to allow Amazon S3 Buckets (via plugins), WordPress does not recognize unregistered files in your file system.
Unfortunately the plugin Real Physical Media does not help here, because it does not implement bidirectional synchronization. That means Real Physical Media allows you to organize your files physically with the WordPress interface.
On the design side of WordPress itself, it’s not a good idea to upload the files via FTP and register them in the media library with any workarounds (e.g. plugins like “Add from Server” or “Media From FTP” can do this). But you should always use the file upload feature provided by WordPress.
What currently prevents you from using the native upload feature of WordPress?
- Increase your maximum allowed file size: https://kinsta.com/blog/wordpress-maximum-upload-file-size/
- Allow certain file extensions for uploading: https://wordpress.org/plugins/wp-add-mime-types/