Update to WordPress 5.5.3 to address an issue introduced in WordPress 5.5.2.
This maintenance release fixes an issue for new WordPress installations where the database connection has not yet been configured.
You can read more by looking at the release notes: https://wordpress.org/support/wordpress-version/version-5-5-3/
You can also see a complete list of changes: https://core.trac.wordpress.org/query?status=closed&resolution=fixed&milestone=5.5.3&order=priority
If you have not done so already – download the update or simply use your existing installation of WordPress to update your site. Either way – this is an excellent time to make a backup copy of your site(s) before upgrading.