Andy Sternberg noticed that when you go to a Google AMP cache page, where it shows the google.com/amp cache URL and not your native URL, the share icon has changed. It is now showing the native sharing icon, as opposed to a drop down that shows you the site's URL.
Andy posted this on Twitter but let me show you the difference as he clarified for me.
Before Google shows this chain link icon that when you clicked on it revealed the site's real URL and you can copy and paste that URL or click on it to see the site on that domain. Here is the screen shot from years ago.
Now, Google just shows the site's real URL and a share icon on the right. When you click it, it gives you the native sharing features and will by default share the site's real URL, not the Google AMP cache URL:
I am not sure when this changed, I do not follow these AMP pages too closely.
Forum discussion at Twitter.
Update: This is not new according to an AMP lead:
This has been around for a while but is only shown if the browser natively supports the navigator.share functionality https://t.co/IpDaCgMgSS
— Malte Ubl (@cramforce) August 21, 2019