Records ten seconds of a moving chessboard and tells you what kind of file your browser produced. Nothing here is real match data. The only question being answered is whether a video comes out and whether your phone will accept it.
The frame number is drawn on the board on purpose. If the numbers skip when you play the recording back, frames were dropped.
On an iPhone, use Share. That is the button that reaches Photos, TikTok and Instagram. Save puts it in Files, which is a different and less useful place.