use get_theme_mod from all sites in network

by

You will have to switch to your blog using switch_to_blog( $blog->blog_id ); and the access the data you want from that blog.

switch_to_blog( $blog->blog_id );
get_theme_mod('your_key');

This should give you customizer option data for that blog.

Also I’m not sure where you are using this code, but instead of using wpdb query you can use get_sites to get list of your sites.

See: https://developer.wordpress.org/reference/functions/get_sites/

Hope this is what you wanted.