WP_Query with all posts in one custom post type and only posts in another custom post type with a specific category

I’m going to take the answer you posted for yourself and suggest a couple of improvements.

Some things I’ll address:

• The 3rd query is unnecessary. There are simpler ways to sort by date. Just make both queries for the full post content and merge the results.
• Since we’re not going to be using have_posts() and the_post() (we’ll use setup_postdata()), we should just use get_posts() to keep things a bit simpler. It should also be a bit quicker as it sets some default query args to optimise it since it won’t need pagination info.
• We’ll avoid repeating ourselves with the query arguments by re-using a single array of arguments.
• We won’t bother specifying arguments that are just the defaults.

Taking those points into account, the code can just be:

$posts_args = [
    'posts_per_page' => $postsnumber,
    'post_type'      => 'post',
];

$posts = get_posts( $posts_args );

$video_args              = $posts_args;
$video_args['post_type'] = 'js_videos';
$video_args['tax_query'] =  [
    [
        'taxonomy' => 'video_category',
        'field'    => 'tag_ID',
        'terms'    => '41',
    ],
];

$videos = get_posts( $video_args );

$combined = array_merge( $posts, $videos );

usort( 
    $combined, 
    function( $a, $b ) {
        return get_post_time( 'U', false, $b ) - get_post_time( 'U', false, $a );
    }
);

global $post;

foreach ( $combined as $post ) : setup_postdata( $post );
    the_title(); // etc.
endforeach;

wp_reset_postdata();