Clipboard write action doesn't work on 6.5.0

When running qutebrowser against webengine 6.5.0 and 6.5.1 various "copy" buttons around the web no longer work.
For example the "Copy Link" button from the three dot menu on comments on GitHub issues: https://github.com/qutebrowser/qutebrowser/issues/7695

(As a point of interest, some copy buttons still do work. For example the code blocks on https://web.dev/async-clipboard/)

We set both QWebEngineSettings.WebAttribute.JavascriptCanAccessClipboard and QWebEngineSettings.WebAttribute.JavascriptCanPaste. When running with the same qutebrowser version and the same settings the Copy Link button on GitHub works fine on 6.4.2 but it has no effect on 6.5.0 and 6.5.1.

In the developer tools running

window.setTimeout(() => {console.log(navigator.clipboard.writeText('hi'))}, 1000)

returns a successful promise on 6.4.2 but the promise never resolves on 6.5.1. So maybe the permission request is getting lost somewhere?

Reading from the clipboard works fine:

window.setTimeout(() => {navigator.clipboard.readText().then(x => console.log(x))}, 1000)