It does before user scroll down the page a little. That's what he called dynamic viewport being added to spec. It was to address issue of incorrect viewport height (100vh) when the toolbar is visible. So units such as svh, lvh, and dvh are added.

Ah gotcha.

But that has been the default behaviour in any mobile browser since forever. I don't know why he would blame Apple for this.

(Though I don't know how it used to interact with vh)

Yeah this is what I was referring to, thanks.