Search results are showing full page instead of sample

Go to theme settings in dashboard (Pokemon -> Layout) and set option “Cut content on the Front/Category page” to ON.

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Update #1

To change the way posts are displayed only on the search page, you can add || is_search() after smt_getOption( 'layout', 'cuttxton' )

if( smt_getOption( 'layout', 'cuttxton' ) || is_search() )

But it will be better to save the changed content.php file under a new name content_search.php:

    <?php if ( !is_single() ) : ?>

        <!-- ========== Post content in posts feed ========== -->
        <div class="entry-summary">
            <?php
                if ( ! post_password_required() ) { 
                    smt_excerpt( 'echo=1' );
                } else the_content( );
            ?>
            <a href="https://wordpress.stackexchange.com/questions/312423/<?php the_permalink(); ?>" class="button"><?php echo smt_translate( 'readmore' ); ?></a>
            <span class="post-categories"><?php the_category(' '); ?></span> 
        </div><!-- .entry-summary -->

    <?php endif; ?> 

    <div class="clear"></div>
</article><!-- #post-## -->

and in search.php use the new template file:

// Start the loop.
while ( have_posts() ) : the_post();

    get_template_part( 'content_search' ); 

// End the loop.
endwhile;

Excerpt lenght

The excerpt lenght can be changed with excerpt_length filter (doc). You can also change length of excerpt in your theme options (“Pokemon” -> “Layout” -> “The default excerpt length”).

Code goes to functions.php:

function custom_excerpt_length( $length ) {
    return 20;  // number of words
}
add_filter( 'excerpt_length', 'custom_excerpt_length', 999 );