The short answer, here, is yes, tuning your new BMW will void your warranty. A tune requires adjustments and sometimes a complete remapping of your vehicle’s ECU factory settings, so you’re literally changing the way it runs.
BMW—and all other manufacturers—guarantee their vehicles based on how they have tuned them to run. That means any changes will negate that guarantee.
Luckily, there are plenty of other aftermarket mod options that won’t void your warranty, as long as they’re properly installed and don’t cause damage to any of your car’s systems. This is a great way to increase your car’s performance without losing your warranty coverage, plus, it can increase your car’s value, leading to some extra cash in your pocket if/when you sell your BMW or trade it in.