> Do search engines (or really just Google) still penalize sites that are pure SPAs on that fact alone?
Google says that they don't. They use an evergreen googlebot, which is the latest (or thereabouts) release of headless Chrome browser; and it waits for the scripts to load and executes them. You can watch Martin Splitt's talk from the recent web.dev live event for the latest updates.
Server-side rendering is still important if you care for other search bots or if you want to share your site's pages on social media (with page preview).
do you have a link to the talk?
Or does it have more do do with properties generally associated with SPAs like large bundle sizes or slow time to first interaction?
I'm mainly wondering if you can build a SEO-friendly SPA marketing page today using techniques like dynamic imports and code splitting to lazy load just the scripts and content needed for the initial render instead of going all the way to static generation or server side rendering.