CiviCRM menu not displaying properly or useably in wordpress
For WordPress 5.5.1 the minimum CiviCRM version is 5.26.2.  I'd recommend 5.28.4 as that is the security release.
Due to changes in WP you may also have to update your settings.
For reference: https://civicrm.org/blog/kcristiano/civicrm-526-and-wordpress-important-notice
Even though the changes discussed come into effect in 5.29 this doc: https://docs.civicrm.org/sysadmin/en/latest/upgrade/version-specific/#civicrm-529  is a good explanation of paths for CiviCRM and WP