Nvidia and AMD both have differing APIs for video decoding. The idea in using Vulkan is that not every GPU supports the vendor specific decoding method, but they do all support Vulkan (modern GPUs, anyways). So this way you still get hardware accelerated decoding through a more widely supported means.

Ventoy isn’t the same. That’s for booting live/installation media but doesn’t typically replace your bootloader in the conventional sense. Or at least, that’s not its intended purpose.

This is intended to replace something like GRUB, the default Linux bootloader for most distributions. It lets you configure the various options or version of a kernel you might like to load, as well as handling the boot options for other operating systems that might be installed.