I don't believe everything nofap bros say but there is some truth to it
Effects of porn/masturbation on brain is very similar to opioid addiction, the receptors of opioids are the same as receptors of acetylcholin, opioid addicts can't feel good without drug because their body produces less acetylcholin in response to opioid, and coom addict only feel good when flooding their limbic system with acetylcholin and dopamine, and in normal state (when not cooming) you'll have low levels of available neurotransmitter
Fast release of neurotransmitters during ejaculation = opioid
An interesting fact: the sections of your brain for mood and emotion is the exact same for mobility, that's why you don't feel like doing anything afterward cooming (low available neurotransmitter)