Disabling auto-resizing of uploaded images

To disable resizing for all image sizes without manually removing each size with remove_image_size function, use the filter intermediate_image_sizes_advanced

/**
 * @param array $sizes    An associative array of image sizes.
 * @param array $metadata An associative array of image metadata: width, height, file.
 */
function remove_image_sizes( $sizes, $metadata ) {
    return [];
}
add_filter( 'intermediate_image_sizes_advanced', 'remove_image_sizes', 10, 2 );