MacOS 10.15 Skim does not pop up

[Uwe Brauer]

I am pretty sure that this is not a stupid method 

I am using the following setting in my custom-init.el
(custom-set-variables
 '(TeX-view-program-list
   '(("PDF Viewer" "/Applications/Skim.app/Contents/SharedSupport/displayline 
-b -g %n %o %b")))
 '(TeX-view-program-selection '((output-pdf "PDF Viewer"))))

However when running C-c C-v or 
C-c C-c select view, the skim view does not pop up but needs to be clicked on

What is the reason?
Any idea for a fix?

Thanks

Uwe Brauer