New image size option not showing

You need to register the image size first using add_image_size(), for example:

add_action( 'after_setup_theme', 'cyb_add_image_sizes' );
function cyb_add_image_sizes() {
    add_image_size( 'my-image-size-name', 120, 120, true );
}

Then, you can use the image_size_names_choose filter (you have misspelled it with image_size_names_chooser):

add_filter( 'image_size_names_choose', 'rudr_new_image_sizes' );
function rudr_new_image_sizes( $sizes ) {

    $addsizes = array(
        "my-image-size-name" => 'Misha size'
    );

    $newsizes = array_merge( $sizes, $addsizes );

    return $newsizes;

}