There's surprisingly little data on this out there that I could find.
The only study I read about was Microsoft's, which doesn't provide concrete data. Microsoft says:
We looked at the icons users were seeing out in the wild and tested
similar variations to see which icons best represented what it meant
to share. We A/B tested them against the old share icon in the Photos
app, with and without labels... The best performing icon was our new
icon, a rectangle housing a swooping arrow that indicates motion out
of the rectangle.
I assume that, as both the three-dot icon that Google popularized and Apple's upward-pointing icon are widely used, Microsoft tested those metaphors out too. And given that the Photos app is on every Windows 10 computer by default, I assume that these tests were on quite a large audience.
The icon they found best represented sharing was icon #2, with a right-pointing arrow.
An opinion piece on Co.Design agrees, though it doesn't have any data to back up its claim. I also find the arrow to be the most representative. It might be because a right-pointing arrow is similar to the forward icon in email clients, which serves basically the same function.
It's also telling that, even though it's not used on iOS anymore, it's still used by Facebook and YouTube (Google's own property) as the share icon, even on Android (as of Dec. 2017). It's also the icon metaphor that FontAwesome, a popular web icon pack, uses.