Hello!
I installed all from scratch and the tt-rss Docker Containers are running on Ubuntu Server 20.04, but the Port 8280 is only open from 127.0.0.1 !
No connection possible from the internal LAN IP of my server (tested directly on the server), so it is no firewall problem!
I changed the variables in .env file to this :
TTRSS_SELF_URL_PATH=http://192.168.0.10:8280/tt-rss
HTTP_PORT=8280
What did i miss , is this a docker configuration failure or a ubuntu server problem ? Perhaps You can help me to solve this problem ! Sorry i have no experience with docker yet and my last Ubuntu install was years ago 
many thanks in advance
theghostofelvis