my solution was in the config file of the nginx-server at “/etc/nginx/sites-available”
listen 4444 ssl http2;
listen [::]:4444 ssl http2;
After the first installation here stands only "listen 4444 ssl; " and “http2” was missing.
A restart of nginx with this parameters it will run and Prosody too.
Thank you, I have now installed the deb installer, which works more or less. Now I can see how it works, I can probably also install it from source. Currently, I am switching from prosody to openfire, I am still figuring out what settings to change in Jitsi.