Please look again at the post, this wasn't a answer for you... Please remove that entry...
Why would you restart SteamCMD? SteamCMD isn't running anyways when step 3 is executed (start the dedicated server), SteamCMD is only needed when the game is donwnloaded/updated.
Please ignore the SDL warning, this has nothing to do with your issue!!!
Is this from the Steam or Epic Game? Something seems to be wrong with the ports when you get this error.
I now noticed that you run this in a custom br0 configuration, can you please try to run this in "bridge" mode instead of "br0" and then connect with your UNRAIDSERVERIP:7777
Something seems wrong with your network configuration, I can only tell you that I just can connect fine to the server and everything is working just fine.