I just tested it on my iPhone 12 Pro.
When using Safari or any web browser, the search function typically begins as soon as you start typing in the search bar. This means that as you type, the browser will attempt to provide search suggestions or even display search results based on the text you've dictated so far.
For example, let's consider the sentence "What does RAM stand for." As you start dictating this sentence, Safari will start searching the web-based on the partial text you've entered. If you pause in the middle of the sentence or take too long to complete it, Safari might assume that you've finished typing and stop the search process. This behavior can be problematic if you're dictating the sentence and need more time to complete it.
To overcome this issue, it's recommended to practice dictation in Safari or any web browser by allowing a brief pause at the appropriate places. By doing so, you give yourself time to finish the sentence before Safari prematurely ends the search process. With practice, you can become more adept at dictating smoothly without interruptions caused by the browser's automatic searching feature.