Guest needs to have spice-guest-tools installed and probably be using gnome - I have had no success with other environments but my testing was shallow.
Alternatively, you can share the host's wayland socket with the guest over the network via waypipe: <https://gitlab.freedesktop.org/mstoeckl/waypipe>
In this scenario the clipboard will function without any issues and with no further steps. And wouldn't require a compositor running in the guest.
You can also have a wayland connection between the guest and host through shared memory buffers via virtio-gpu. But this requires crosvm as qemu doesn't have this functionality. Guest kernel needs to be >=5.16 and be compiled with CONFIG_DRM_VIRTIO_GPU and this tool is required: <https://github.com/talex5/wayland-proxy-virtwl>