Thank you, Nergal
I did upgrade from CC v5.25 to v5.26 and then I could delete the coockie permanently.
I also discovered that I caught this coockie when I tried to reach
" https://secure.piriform.com/ " but then the website
" https://support.cleverbridge.com/hc/de/requests/new?ticket_form_id=18434 "
opened.
Problem solved - thanks again.
When deleting cookies the cookie "s.uicdn.com" is only temporarily gone, when rechecking the cookies it appears again.
The computer is not connected to the internet while deleting - so the cookie is stored somewhere.
Any ideas to delete this permanently, please?