As I wrote in the headline: The option in Windows Explorer to share a public link is gone since client version 3.15 (I guess):
In the WebUI everything works fine.
Hi @wwessel
What happens when you click on “Freigabeoptionen”?
Hi @bb77
I get this:
There I can click on “Link teilen” (Share link) +, but I can’t copy this link anywhere, only on the WebUI.
BTW: This all worked fine before update to client 3.15…
Interesting. I didn’t have the button the first time I tried it.
But after I restarted my PC, it appeared as in your screenshot.
So it’s not a bug, it’s a feature?
For me it seems to be a buggy feature.
Apart from being cumbersome because it requires more clicks, it is buggy because the sharing window does not open in the foreground and an empty button is displayed after clicking on Copy
Seems like it.
I can’t reproduce either of the problems you describe, but perhaps you could open a separate thread for them, describing them in more detail, or file a bug report on GitHub. You might also want to try rebooting your computer first, if you haven’t done so already 
I can confirm the issue with 12/12 Windows machines and 3/3 Macs I have used since the update.
They are connected to different servers using virtual drive and also conventional sync.
This can’t possibly be a feature.
The feature is the ‘Share’ dialog with the ‘Copy’ button, as shown in my screenshot. However, if the dialog opens in the background, or if an empty button is displayed after clicking the Copy button, as @GTL experienced, these would of course be bugs that should be reported.