I don’t know why categories are showing below post

I assumed that your are using undersocres starter theme to build your theme
and you probably copied the code from template-tags.php inside inc folder in your theme.
Now do this:

keep this code inside template-tags.php

function category_renown() {
    $categories = get_the_category_list( esc_html__( ' ', 'openblogger' ));
    if ( $categories ) {
            printf( '<span class="catu-links">' . esc_html__( '%1$s', 'openblogger' ) . '</span>', $categories ); // WPCS: XSS OK.
        }
}

copy your function inside content.php file like:

this is the content for content.php file

<?php
/**
 * Template part for displaying posts
 *
 * @link https://developer.wordpress.org/themes/basics/template-hierarchy/
 *
 * @package xyz
 */

?>

<article id="post-<?php the_ID(); ?>" <?php post_class(); ?>>
    <header class="entry-header">
        <?php category_renown(); ?>
        <?php
        if ( is_singular() ) :
            the_title( '<h1 class="entry-title">', '</h1>' );
        else :
            the_title( '<h2 class="entry-title"><a href="' . esc_url( get_permalink() ) . '" rel="bookmark">', '</a></h2>' );
        endif;

        if ( 'post' === get_post_type() ) :
            ?>
            <div class="entry-meta">
                <?php
                xyz_posted_on();
                xyz_posted_by();
                ?>
            </div><!-- .entry-meta -->
        <?php endif; ?>
    </header><!-- .entry-header -->

    <?php xyz_post_thumbnail(); ?>

    <div class="entry-content">
        <?php
        the_content( sprintf(
            wp_kses(
                /* translators: %s: Name of current post. Only visible to screen readers */
                __( 'Continue reading<span class="screen-reader-text"> "%s"</span>', 'xyz' ),
                array(
                    'span' => array(
                        'class' => array(),
                    ),
                )
            ),
            get_the_title()
        ) );

        wp_link_pages( array(
            'before' => '<div class="page-links">' . esc_html__( 'Pages:', 'xyz' ),
            'after'  => '</div>',
        ) );
        ?>
    </div><!-- .entry-content -->

    <footer class="entry-footer">
        <?php xyz_entry_footer(); ?>
    </footer><!-- .entry-footer -->
</article><!-- #post-<?php the_ID(); ?> -->

now you need to remove the following code in template-tags.php file inside function xyz_entry_footer():

$categories = get_the_category_list( esc_html__( ' ', 'openblogger' ));
if ( $categories ) {
        printf( '<span class="catu-links">' . esc_html__( '%1$s', 'openblogger' ) . '</span>', $categories ); // WPCS: XSS OK.
    }

final version of template-tags.php should be:

<?php
/**
 * Custom template tags for this theme
 *
 * Eventually, some of the functionality here could be replaced by core features.
 *
 * @package xyz
 */

if ( ! function_exists( 'xyz_posted_on' ) ) :
    /**
     * Prints HTML with meta information for the current post-date/time.
     */
    function xyz_posted_on() {
        $time_string = '<time class="entry-date published updated" datetime="%1$s">%2$s</time>';
        if ( get_the_time( 'U' ) !== get_the_modified_time( 'U' ) ) {
            $time_string = '<time class="entry-date published" datetime="%1$s">%2$s</time><time class="updated" datetime="%3$s">%4$s</time>';
        }

        $time_string = sprintf( $time_string,
            esc_attr( get_the_date( DATE_W3C ) ),
            esc_html( get_the_date() ),
            esc_attr( get_the_modified_date( DATE_W3C ) ),
            esc_html( get_the_modified_date() )
        );

        $posted_on = sprintf(
            /* translators: %s: post date. */
            esc_html_x( 'Posted on %s', 'post date', 'xyz' ),
            '<a href="' . esc_url( get_permalink() ) . '" rel="bookmark">' . $time_string . '</a>'
        );

        echo '<span class="posted-on">' . $posted_on . '</span>'; // WPCS: XSS OK.

    }
endif;

if ( ! function_exists( 'xyz_posted_by' ) ) :
    /**
     * Prints HTML with meta information for the current author.
     */
    function xyz_posted_by() {
        $byline = sprintf(
            /* translators: %s: post author. */
            esc_html_x( 'by %s', 'post author', 'xyz' ),
            '<span class="author vcard"><a class="url fn n" href="' . esc_url( get_author_posts_url( get_the_author_meta( 'ID' ) ) ) . '">' . esc_html( get_the_author() ) . '</a></span>'
        );

        echo '<span class="byline"> ' . $byline . '</span>'; // WPCS: XSS OK.

    }
endif;

if ( ! function_exists( 'xyz_entry_footer' ) ) :
    /**
     * Prints HTML with meta information for the categories, tags and comments.
     */
    function xyz_entry_footer() {
        // Hide tag text for pages.
        if ( 'post' === get_post_type() ) {

            /* translators: used between list items, there is a space after the comma */
            $tags_list = get_the_tag_list( '', esc_html_x( ', ', 'list item separator', 'xyz' ) );
            if ( $tags_list ) {
                /* translators: 1: list of tags. */
                printf( '<span class="tags-links">' . esc_html__( 'Tagged %1$s', 'xyz' ) . '</span>', $tags_list ); // WPCS: XSS OK.
            }
        }

        if ( ! is_single() && ! post_password_required() && ( comments_open() || get_comments_number() ) ) {
            echo '<span class="comments-link">';
            comments_popup_link(
                sprintf(
                    wp_kses(
                        /* translators: %s: post title */
                        __( 'Leave a Comment<span class="screen-reader-text"> on %s</span>', 'xyz' ),
                        array(
                            'span' => array(
                                'class' => array(),
                            ),
                        )
                    ),
                    get_the_title()
                )
            );
            echo '</span>';
        }

        edit_post_link(
            sprintf(
                wp_kses(
                    /* translators: %s: Name of current post. Only visible to screen readers */
                    __( 'Edit <span class="screen-reader-text">%s</span>', 'xyz' ),
                    array(
                        'span' => array(
                            'class' => array(),
                        ),
                    )
                ),
                get_the_title()
            ),
            '<span class="edit-link">',
            '</span>'
        );
    }
endif;

function category_renown() {
    $categories = get_the_category_list( esc_html__( ' ', 'openblogger' ));
    if ( $categories ) {
            printf( '<span class="catu-links">' . esc_html__( '%1$s', 'openblogger' ) . '</span>', $categories ); // WPCS: XSS OK.
        }
}
if ( ! function_exists( 'xyz_post_thumbnail' ) ) :
    /**
     * Displays an optional post thumbnail.
     *
     * Wraps the post thumbnail in an anchor element on index views, or a div
     * element when on single views.
     */
    function xyz_post_thumbnail() {
        if ( post_password_required() || is_attachment() || ! has_post_thumbnail() ) {
            return;
        }

        if ( is_singular() ) :
            ?>

            <div class="post-thumbnail">
                <?php the_post_thumbnail(); ?>
            </div><!-- .post-thumbnail -->

        <?php else : ?>

        <a class="post-thumbnail" href="<?php the_permalink(); ?>" aria-hidden="true" tabindex="-1">
            <?php
            the_post_thumbnail( 'post-thumbnail', array(
                'alt' => the_title_attribute( array(
                    'echo' => false,
                ) ),
            ) );
            ?>
        </a>

        <?php
        endif; // End is_singular().
    }
endif;

I just assumed you are building theme using underscores starter theme. If not please add more code ( where you are calling that function )

another thing you may have done more changes to starter theme, so be careful before copying and pasting this code.

error code: 523