Ok thank you @gotwf
Also looks like I spoke too soon - regarding your original question 1, if I bypass nginx and connect directly using the server external ip to port 4567, I can see nodebb launch "correctly". But if I access it through the domain name, it gives me the above result. So that did matter.
Here is the nginx server block (file name - forum.kado.ai.conf)-
Here is the nodebb config file.