This is not supported for Windows or WebAssembly yet.
It's possible for applications to post to the clipboard using
Screen.SetClipboard (any data), and they can retrieve the clipboard
(if permitted) using GetClipboard. The terminal may well reject either
of these.
Retrieval will arrive as a new EventClipboard, if it can. (There is
no good way to make this synchronous.)
This work was inspired by a PR submitted by Consolatis (#562), and
has some work based on it, but it was also substantially improved and
now includes both sides of the clipboard access pattern.
Garrett D'Amore