Thanks Jacky_W Your post gave me a hint in the right direction. Fiddled around with different plugins and eventually the reader connected as “User defined USB-device” . Better but not good yet. Reinstalled Calibre, still the same. Finally deinstalled Sony Reader and all instances of Calibre (also in users/appdata/roaming ) and reinstalled Calibre again.
Did the wellknown, usual settings and guess what……..the reader connected automatically as “Sony Reader” and in “Device” a collection is present. Hurrah, hurrah. Thanks all for the joined thinking, posts, advises, remarks.