Summer solstice 2024 marks the longest day in the Northern Hemisphere

Yes, she means the longest period of daylight.

But, Earth's actual solar day length is not set at exactly 24 hours. Because the Earth has a slightly elliptical orbit, it moves faster when closer to the Sun and slower when farther away. But, it rotates at a pretty constant rate. So, the extra amount of rotation that the Earth needs to do to get back to solar noon on the same point on its surface varies between Earth's perihelion and aphelion. On the other hand, a sidereal day, which measures the amount of Earth's rotation against distant stars, remains the same over the year, and is shorter than 24 hours.