Original image not saving?

The default image sizes of WordPress are “thumbnail”, “medium”, “large” and “full” (the size of the image you uploaded). These image sizes can be configured in the WordPress Administration Media panel under Settings > Media. This is how you can use these default sizes with the_post_thumbnail():

the_post_thumbnail();                  // without parameter -> 'post-thumbnail'

the_post_thumbnail( 'thumbnail' );       // Thumbnail (default 150px x 150px max)
the_post_thumbnail( 'medium' );          // Medium resolution (default 300px x 300px max)
the_post_thumbnail( 'large' );           // Large resolution (default 640px x 640px max)
the_post_thumbnail( 'full' );            // Full resolution (original size uploaded)

the_post_thumbnail( array(100, 100) );  // Other resolutions

for more information to see https://developer.wordpress.org/reference/functions/the_post_thumbnail/