As some tips from the forum have also helped me with this...

Here are my finished CWCs for detecting mobile devices and detecting the user agent used.

The recognised user agent or the boolean variable "Mobile Device" can be read out in the "writeValue" event:

let sysagent = Tags("SYS_USERAGENT");
sysagent.Write(AgentName);

Hope it helps and maybe somebody even helps extending it's functionality