I've been using gmail since the early beta days and was never aware of this functionality. But on closer inspection there appears to be a highly stylized (unrecognizable) camera icon there that takes me to, I guess the long lost cousin of Google Meet?? Why are these apps welded together? What a bizarre decision. I thought Meet went to The Graveyard along with Allo and Duo and Wave.
Meet was discontinued; its functionality was merged into Duo and the resulting app renamed to Meet.
My work uses GSuite so I’m using Meet every day. I find it mildly useful to have the functionality built into the Gmail app but at the same time I see zero loss in having it be a separate app.