If you want OnePlus 8 Windows Drivers for Fastboot, you need to install the Universal ADB Driver, which packs all of the commonly used USB Drivers into one file.
You may also be interested in using Minimal ADB and Fastboot. The minimal version of ADB and Fastboot gives you the ADB and Fastboot within the rest of the Android SDK package.
Fastboot works by booting into Bootloader/Fastboot Mode. You can use Fastboot to flash system partitions, though you must unlock the device’s bootloader before you do this. Fastboot and ADB are commonly requested by those looking to get root access or install a custom recovery image on a smartphone.
The OnePlus 8 smartphone can be rooted by using Magisk. When you use Magisk, it won’t install any custom recovery image or custom boots. The rooting method for the OnePlus 8 is different from many others and requires the lineage-18.1-20210606-recovery-instantnoodlep.img or a newer version of the same image.