How to allow html tags in the_excerpt post function in wordpress

Just copy and paste below code into your theme's functions.php file or in your custom plugin file.
and change according to your need.

function rj_wp_trim_excerpt($text) {
$raw_excerpt = $text;
if ( '' == $text ) {
    $text = get_the_content('');
    $text = strip_shortcodes( $text );

    $text = apply_filters('the_content', $text);
    $text = str_replace(']]>', ']]>', $text);
    
    $allowed_tags = '<p>,<a>'; // write your tags here for allow them in excerpt with comma seprated
    $text = strip_tags($text, $allowed_tags);
    
    $excerpt_word_count = 55; // change length of excerpt according to your need
    $excerpt_length = apply_filters('excerpt_length', $excerpt_word_count);
    
    $excerpt_end = '[...]';
    $excerpt_more = apply_filters('excerpt_more', ' ' . $excerpt_end);
    
    $words = preg_split("/[\n\r\t ]+/", $text, $excerpt_length + 1, PREG_SPLIT_NO_EMPTY);
    if ( count($words) > $excerpt_length ) {
        array_pop($words);
        $text = implode(' ', $words);
        $text = $text . $excerpt_more;
    } else {
        $text = implode(' ', $words);
    }
}
return apply_filters('wp_trim_excerpt', $text, $raw_excerpt);
}
// disable default wordpress function by remove_filter
remove_filter('get_the_excerpt', 'wp_trim_excerpt');
add_filter('get_the_excerpt', 'rj_wp_trim_excerpt');