This doesn’t seem to be good advice. My WP 4.9 runs under PHP 5.2, but WP 5.9 does not. And WP 5.9 runs under PHP 7.4, but WP 4.9 does not. It’s not necessarily true that you can one-click upgrade from 4.9 to 5.9.
Would it be possible to update the plugin (or create a new one) based on the RSS feed?