Supplements are generally a controversial subject with lots of doubt on which works and which doesn't. I can't personally guarantee the following will work for you, but after trial and error of lots, these are the ones I personally found useful.
This supplement is used for calming the brain and increasing focus at the same time. I have found it actually works wonders for helping me to stay focused, reduce stress and even has a synergy effect with caffeine. Multiple studies have shown the positive effects it has had on brain focus. The great thing about this is it pairs with caffeine, so if you get a bit jittery from caffeine this will work wonders for you. I have used it to even reduce my anxiety when not working as well. A lot of proven studies have shown this synergy.
This is a very interesting mushroom. In fact it's called the intelligence boosting mushroom. It promotes the growth of new brain cells and makes new connections faster. It has shown to reduce the symptoms of Dementia and Alzheimer's. For me personally? I found my intelligence being boosted by taking it daily before learning new coding concepts. I was able to understand things faster, make connections quicker and even my chess ELO has been improving. Of course sometimes these things can be a placebo, but if you value my opinion it's worth giving a shot.
This compound is found naturally and very high in beetroot. I personally love beetroot and found it had an effect at lowering your blood pressure, specially around workouts. I trialed taking this with my day to day work and found myself more relaxed and recovering better from my weightlifting. This supplement has many proven effects. I ordered the capsules and now it's part of my daily use, I have more energy, my workouts are longer and I seem to have more energy during long programming sessions.
This one is obvious, most people already use this to boost mental focus. I find overdoing it leads to burnout very quick, so it's best to keep your dosage small to stop any addiction forming habits. Also always pair it with L-theanine mentioned above to boost its effects. You can also get it more naturally in things like green tea. Try keep your dosage below 80mg per day or you will start to get into the negative effects and crashes.
Nothing in life is a silver bullet that will make you magically better. However if you take these things, exercise regularly and eat a healthy diet you will find you will become better at coding or any other mentally exhausting activity......like writing these articles ;)