via make.wordpress.org => original post link
Prior to the WordPress 6.0 release plugin and theme developers used the do_parse_request filter to hot-wire requests and hook in early to render custom pages. Not needed post queries and 404 lookups were still run. This resulted in unnecessary SQL queries running on these requests.
The change
In 6.0 we added a return value to the parse_request method of the WP class. These queries are not needed and now skipped if false is returned by the do_parse_request filter.