Change the default template of page and post to something else

functions.php

/**
 * Change the default template to elementor_header_footer for new page and post
 */
function bb_rest_set_default_page_template( $data, $post ) {
    if ( 
        0 != count( get_page_templates( $post ) ) 
        && get_option( 'page_for_posts' ) != $post->ID 
        && '' == $data->data['template']
    ) {
        $data->data['template'] = 'elementor_header_footer';
    }
    return $data;
}
foreach ( array( 'page', 'post' ) as $post_type ) :
    add_filter( "rest_prepare_{$post_type}", 'bb_rest_set_default_page_template', 1, 2 );
endforeach;