But what exactly is the "Preloader"? Is it a virus? A hardware failure? Or simply a software hiccup?

The phone shows the Xiaomi logo and then restarts repeatedly.

Before you can fix the Redmi 9c, your PC must communicate with the preloader without disconnecting. Windows often blocks the driver because it detects the rapid on/off cycle as a malfunction.

The Redmi 9C often employs A/B partition slots (seamless updates). This means there are often two sets of boot partitions. However, the Preloader remains the critical starting point. If the Preloader is corrupt, the phone cannot even access the recovery mode or fastboot mode.

If you are a developer or a power user, you might want to extract the preloader binary from your working Redmi 9c to flash to a bricked one.