How do immersive sites still score 80–90+ on PageSpeed?
By rendering on the server and splitting the heavy code out of the critical path. The crawler gets a complete HTML document, the visitor gets the full animated experience, and neither one waits on the other.
Three things do the work: server-side rendering (the document arrives complete, so a bot scans real headings instead of waiting on JavaScript), bundle separation (shaders, 3D, and motion engines load once the page is usable), and restrained motion (the main thread stays free during the moments the score is measured).
That said, not every template is SEO-optimised out of the box — some will still need work from your side.
When to use it
Read this when someone tells you an animated site can't rank — or before you rebuild a layer client-side and undo the work.