I installed Windows 10 in a Boxes virtual machine. I enabled shared clipboard, but I am unable to copy/paste from PureOS to Windows.
Have you tried the suggestion in this link?
While express installation typically takes care of making shared clipboard available to you, express installation is not available for all operating systems. In such cases or if you choose manual installation, for shared clipboard to work the SPICE vdagent needs to be installed in the guest. In most Linux-based operating systems the package is called spice-vdagent. If the guest is running a different operating system, check out the SPICE download page.
Thank you! I installed the Windows guest tools in my Win10 VM, and I can copy/paste from PureOS now.