Creatine crosses the blood-brain barrier and improves cognitive performance.

Study: The effects of creatine supplementation on cognitive performance—a randomised controlled study

Taking creatine for six weeks slightly improved memory in a small test, but didn't help with other thinking tasks. It's not a big boost, but it might help a little — and it didn't hurt.

Study: Effects of Creatine Monohydrate Loading on Sleep Metrics, Physical Performance, Cognitive Function, and Recovery in Physically Active Men: A Randomized, Double-Blind, Placebo-Controlled, Crossover Trial

This study found that people who took creatine for a week did better on a memory and attention test, suggesting creatine helps the brain work better. It doesn't prove creatine gets into the brain, but better thinking after taking it makes it likely.

Study: Effects of high-load, velocity-intentional variable resistance training combined with creatine supplementation on neuroplasticity, oxidative stress, inflammation, physical function, cognitive performance and quality of life in older adults: A randomized, double-blind, placebo-controlled trial

Creatine didn't directly test brain entry, but it helped older people feel healthier and improved brain-related markers like inflammation — which only happens if creatine gets into the brain. So yes, it likely helps the brain work better.