Fire OS does not support UEFI or BIOS booting. Your PC’s processor (x86) cannot execute ARM code natively without massive emulation overhead. Even if you force it, there are no storage or input drivers.
The safest and most reliable source for Fire OS firmware is directly from Amazon. fire os iso download
If you want a clean Android experience on a Fire Tablet, use the Fire Toolbox to debloat the existing system. If you want to install a fresh OS, visit the XDA Developers forums for your specific device model to see if a custom ROM (like LineageOS) has been ported to it. Fire OS does not support UEFI or BIOS booting