To include an HTML button element that is hidden, developers have a few choices. Unless an input element has "hidden" as its "type" attribute, it will appear within the page by default.

It’s next to the existing microphone icon in Google’s four colors for voice input. Update 8/6 : After first spotting in late June, the Google Search button A/B test disappeared on my account ...

The main input screen (from the Search bar shortcut) now has a microphone icon next to the submit button. It joins the gallery to add existing images and Google Lens on the left side.