@ChuckPa
thanks for your fast feedback. done like this just removed the sudo - because i do not have sudo
curl https://downloads.plex.tv/plex-keys/PlexSign.key | apt-key add -
% Total % Received % Xferd Average Speed Time Time Time Current
Dload Upload Total Spent Left Speed
0 0 0 0 0 0 0 0 --:–:-- --:–:-- --:–:-- 0E: gnupg, gnupg2 and gnupg1 do not seem to be installed, but one of them is required for this operation
100 3072 100 3072 0 0 18731 0 --:–:-- --:–:-- --:–:-- 18731
(23) Failed writing body
also to install the software worked fine
but how to start the webgui with no registration, the server is just in my LAN with only access to my NAS where all the film are stored