By definition, is a low-power state designed to save energy. To do this, the computer cuts power to most components, including the processor (CPU) and the network card (Wi-Fi or Ethernet). Since the hardware required to move data from the internet to your hard drive is "asleep," the download pauses. The Exception: Modern Standby
When a computer wakes up from sleep mode, any paused processes, including downloads, should resume where they left off. However, this depends on the specific application and operating system configuration. when computer is in sleep mode does it still download
Sleep is for pausing your work, not your downloads. By definition, is a low-power state designed to save energy
Here’s a detailed feature article covering the question: The Exception: Modern Standby When a computer wakes
If your PC supports Modern Standby, it can download updates, but it is often restricted to "official" Windows updates rather than your Steam library or a browser download. How to Make Your Computer Download While "Asleep"