For version 1.2.x:
Not sure on a QNAP since I don’t have one. The Gitlab page for Roon Web Controller has information about both command line options and a config file. Looks like @BlackJack gave a good answer here: How to: Install Roon Extension Manager on QNAP
For 2.0.0:
You can’t yet. I will be implementing environmental settings to configure the port though. This is mainly for docker/kubernetes support but should also be useful in other setups.
Can the QNAP set/use environmental variables? If not, I will also investigate a file based way to set the port.