To check what’s being used in your session, you can look in the C-*/session logs.
If you get:
Info: Using H.264 software encoder.
the encoding is done by the CPU, otherwise you’ll get “hardware encoder” if it is done by the GPU.
If there is no H.264 encoding available on the server, it will fall back to VP8 and in the panel you mention, you will see VP8, not H.264.
More info about H.264 is here:
Enabling the H.264 codec on the NoMachine client host https://www.nomachine.com/AR10K00696
What do I need to do to allow NoMachine software to use H.264? – https://www.nomachine.com/AR10K00696