How does WordPress determine if a server supports pretty permalinks?

Given that httpd is a very minor webserver by market share and didn’t support rewrites until OpenBSD 6.6, it’s not really surprising that WP hasn’t been written to accommodate it.

The basic structure that WP requires is if the request is not for an extant file or directory, to rewrite it to index.php in the root of the site. You’re going to have to implement that yourself. The guide at openbsdhandbook.com only acknowledges OpenBSD 6.4, so obviously there’s no mention there of how it implements rewrites.

Otherwise, it might be a better idea to use a supported and better documented webserver like nginx.

Digging into it a little further: the actual test for rewriting is carried out by got_url_rewrite(), which by default returns true if one of the below conditions is satisfied:

• Apache’s mod_rewrite module is loaded
• $GLOBALS['is_nginx'] is set
• $GLOBALS['is_caddy'] is set
• iis7_supports_permalinks() returns true

Provided you have rewrites correctly configured the below should work for you:

function wpse427660_got_rewrite() {
    return true;
}

add_filter( 'got_url_rewrite', 'wpse427660_got_rewrite' );