Thank you very much for your informative answer. Disabling desktop effects didn´t work. As a non-techie with spare time resources, I will not try this on my own. I know that there would be many people who probably need a working solution and benefit from my possible success, but I spend the last three days haggling with the current drop of nvidia 340xx drivers. I even had to install manjaro anew and will try out phillims solution posted here:
or downgrade to an older kernel,
or install a different Distro like Kubuntu. (Even considering this, is hurting myself as much as it is probably hurting any reader here 
)