The View Transitions API is available as a first public working draft. The purpose of the API is to allow transitions between the loading of pages of a website – for Single Page Apps (SPA) as well as for Multi Page Apps (MPA). Smooth transitions for loading pages would allow a traditional website to be perceived very much like a native app and would improve how a user perceives the website logic. It's a great improvement in my view but it is impossible to do it properly today, especially for MPAs. Once fully available, the API would allow transitioning between server-side rendered pages without using any JavaScript.
A first implementation of the API is available in Chrome 104+ behind the feature flag chrome://flags/#document-transition. Maxi Ferreira made an excellent example of its usage: Experiments with Astro and the Shared Element Transition API.
When you jump to Maxi's Room For Improvement section you find there is still some work to do. So much so, that unfortunately for now I'm not going to invest time into that. But once it's stable, I think it will quickly turn into a must-have for websites.
There is more material by Jake Archibald with his article Smooth and simple page transitions with the shared element transition API, and the below video: