Describe the feature you'd love to see

The documentation of the View Transitions API available in Chrome 111+ has a section Working with frameworks which mentions React's flushSync function as a key to use it together with the View Transitions API.

Because when using startViewTransition, you have to ensure that the DOM is completely updated, which is what flushSync does.

Preact's implementation of flushSync however is currently just a no-op.

So my suggestion is to implement flushSync so that it ensures that the DOM is updated completely like described here.