I'm targeting to deploy a mesh network and manually configure MANET routing protocols. I'm preparing scenarios, architectures, and hard devices needed to do that. Are there some step-by-step guidelines?
then you should take a look at "Ubuntu Core", very good for embedded environments, optimised for security and with good working updates.
Another OS could be "Raspberry Pi OS Lite", which is the smallest from Raspberry Foundation themself.
Both are rather small and you can configure them to start without GUI. Just leave the GUI on the card and don't use if you don't need it. I think for development it would be good to have the GUI, but for running MANET routing a GUI would not be necessary, it would be even more power consuming.