It could be permissions problem or missing directory. Try pre-creating /var/run/spice-vdagentd (settings permissions/owner as necessary). If it works then, you need to open bug report.
The recommendation in the openSUSE community docs which is the same as the top answer in your reference is to configure a virtual tablet instead of a virtual mouse and in the case of openSUSE also install the touchscreen packages.
Personally, I haven’t fully investigated the consequences of this setting, from a Developer’s point of view touch gestures while appearing on the surface are similar to mouse movements and clicks, are very different.
For example, “Touch and hold” normally should be the equivalent to a Rt-click, but when developing an application the code is very different. I don’t know if <all> normal applications would automatically translate these different actions.
But yes, I can see how a display emulating touch would “activate” differently and possibly automatically when “touched” instead of locking the mouse focus.
Re-reading the title of your post,
These steps to configure your Guest as a tabletpc to enable “touch” gestures replacing click mouse events only addresses the mouse, it won’t do anything for sharing clipboard contents.
AFAIK libvirt should support a common clipboard between Host and Guest by default already, if it’s broken then you may want to mount a shared folder and paste content to a common storage.
