Re: Missing lib?
Those instructions are out-of-date. On 5.4 with an up-to-date ports tree, I did not install linux_mesa but linux_dri instead. I installed the nVidia driver and nwnclient from ports.
Looking at the linux-nwnclient port, I see the proper thing to do is to install it this way to have all of the necessary libraries:
make WITH_NVIDIA_GL=yes install