This helped me. I’ve needed to change some things because I have “SSH & Web Terminal” from Community instead of official “Terminal & SSH”.
In step 2: Find container name for my addon with:
docker ps
Change container name and folder when copying:
docker cp addon_xxxxx_ssh:/etc/ssh/authorized_keys .
Step 3:
systemctl start dropbear
And just no problems with ssh root@my_ip -p 22222