Score is now great, 96 for mobile and 99 for desktop, however Search Console still report errors because they think the pages are slow accroding to First Contentful Paint (FCP) or First Input Delay (FID).
Discourse is a big web app and will never rank as fast as a simple blog or static HTML page. That is a know off trade-off made on the beginning of the project. It’s more akin to Slack/Discord/GMail/Facebook than to HackerNews or https://perfectmotherfuckingwebsite.com/.
We have several plans to alleviate this next year, dropping support for IE for example, and also the EmberJS people said that bundle size is their next big thing as they launched their last big feature this week.
But in the end, if your priority is having a better score on that now, better use a different software.