It was extremely annoying, but, as
@pdwestman says, if you click "OK" it will change your view to "Card View" and won't pop up again.
I haven't the faintest idea what "Card View" is nor why we should be excited and pleased that it has entered our lives and made stuff 27% better than real life.
If you don't like being 27% better than real life you can change it back to what they say it was before, though I couldn't swear to it. Go to the three-dot menu next to your avatar at the upper right-hand corner of this page. Scroll down to "View Mode" and select "Comfort" instead of "Card(Beta)".