On March 27, 2021, 56 y.o. Budimir Šobat (Croatia) broke the record for the longest time breath held voluntarily (male) with a staggering time of 24 minutes 37.36 seconds.
How the heck do people hold their breath for that long?
First you need to know that there are multiple different records for breath holding. The record that is at 24 minutes is one where you are allowed to breath pure oxygen for a certain of amount time prior to your attempt. This greatly increases the amount of oxygen in your blood. However the record where they use normal air is still at around 13 minutes.
There are a couple techniques involved in holding your breath. One of the most important things in making holding your breath easier is a low amount of carbon dioxide. Contrary to what you might think, it is high levels of CO2 that tells your body that you need to breathe and invokes the impulse of breathing. So the way to make holding your breath as easy as possible is to lower you levels of CO2 and preventing it from going up.
Lowering your CO2 levels is done by breathing exercises. Hyperventilating on purpose rids the body of CO2 and makes it a lot easier to hold your breath for extended periods of time.
Next you will want to use as little oxygen as possible. This means staying as still as possible. Not even the slightest movements. You will also want to lower your metabolic rate since this also takes oxygen. You can do this by simply fasting for a while before your attempt.
Lowering your heart rate also prevents oxygen from being used to quickly. To give you an idea when David Blaine trained for his world record attempt he had a heart rate at rest of about 38 beats per minute (unfortunately during his actual attempt it never went down below 100 until the very end)
Of course on top of that having lots of oxygen in your body is just as important. Oxygen is carried in the blood by red blood cells and having more red blood cells means more oxygen is able to be in your blood. Your body automatically makes more red blood cells if you live in a oxygen rare atmosphere like high in the mountains. This is usually just done artificially with practice in low pressure rooms.
You also just have to practice ignoring the impulse to breath. It takes some pretty insane self control and motivation to do this well and it’s of course very risky.
Most of this information comes from the TED talk David Blaine gave and my own interest in free diving and breath holding.