Unexpected very slow user count in WordPress
Add this composite index to wpe_posts:  INDEX(post_status, post_type, post_author).
The answer to &quot;why&quot;:  In 5.5 (and before), IN ( SELECT ... ) was a terribly slow construct.
Amd see if this runs faster:
SELECT  SQL_CALC_FOUND_ROWS wpe_users.*
    FROM  ( SELECT  DISTINCT post_author
            FROM  wpe_posts
            WHERE  post_status = 'publish'
              AND  post_type IN ( 'post', 'page', 'attachment',
                        'wp_block', 'products' ) 
          ) AS x
    JOIN wpe_users USING wpe_users.ID = x.post_author
    ORDER BY  display_name ASC
    LIMIT  0, 10;

For further discussion, please provide EXPLAIN SELECT ... and SHOW CREATE TABLE.
Be aware that a future version is likely to remove the SQL_CALC_FOUND_ROWS feature, forcing you to make two SELECTs.