yeah most supplements don’t really past the sniff test (placebos), but creatine is one that has a decent mass of evidence for it’s efficacy in training. You are right it acts as a buffer, although I am not certain there is a threshold of intensity. I think it’s more if there is bindable phosphor it can occur and allow reuse.

I haven’t read over this entirely yet, but it seems more in line with your particular interest wrt creatine and brain function.

There is a robust and compelling body of evidence supporting the ergogenic and therapeutic role of creatine supplementation in muscle. Beyond these well-described effects and mechanisms, there is literature to suggest that creatine may also be beneficial to brain health (e.g., cognitive processing, brain function, and recovery from trauma). This is a growing field of research, and the purpose of this short review is to provide an update on the effects of creatine supplementation on brain health in humans. There is a potential for creatine supplementation to improve cognitive processing, especially in conditions characterized by brain creatine deficits, which could be induced by acute stressors (e.g., exercise, sleep deprivation) or chronic, pathologic conditions (e.g., creatine synthesis enzyme deficiencies, mild traumatic brain injury, aging, Alzheimer’s disease, depression). Despite this, the optimal creatine protocol able to increase brain creatine levels is still to be determined. Similarly, supplementation studies concomitantly assessing brain creatine and cognitive function are needed. Collectively, data available are promising and future research in the area is warranted.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7916590/