Change WordPress’ Big Image threshold or disable it altogether

Completely disable image size threshold

add_filter( 'big_image_size_threshold', '__return_false' );

Increase the image size threshold to 4000px

function custom_image_threshold( $threshold ) {
   return 4000; // new threshold
}
add_filter('big_image_size_threshold', 'custom_image_threshold', 999, 1);