unknown issue in ‘header.php’ preventing theme from displaying fully

wp_lists_pages is not a valid function, it’s wp_list_pages (no s at end of list).

enable debugging in your wp-config.php file to see php errors

Edit: additional ifo

To answer your other question most advanced editors will check the syntax in your code and will flag errors. With a function spelling error you would need an advanced IDE like PhpStorm to check core WordPress functions and do code completion while you type.

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