Requirements:

Installed Chaotic-AUR repositories
Already installed Windows on KVM (or any other OS)
2 GPUs (dedicated and iGPU works too)
Virtualization and IOMMU enabled in your BIOS/UEFI
An HDMI cable connected to your motherboard if you have an iGPU as a second GPU

MAKE SURE TO READ EVERYTHING FIRST BEFORE CONTINUING AND ENSURE YOU UNDERSTAND EVERYTHING SHOWN

Install KVM if not already done:

sudo pacman -S qemu-full virt-manager bridge-utils libguestfs dnsmasq vde2 openbsd-netcat && sudo systemctl enable libvirtd && sudo systemctl start libvirtd && sudo usermod -aG kvm $USER && sudo usermod -aG libvirt $USER && sudo virsh net-start default && sudo virsh net-autostart default

Install the VFIO Linux Kernel:

sudo pacman -S linux-vfio linux-vfio-headers

Get Your GPU IDs:

lspci -nn | grep -E "NVIDIA"

Trim the IDs and separate them with commas (,) only.
Save the IDs somewhere.
You will need both your GPU ID and your GPU audio device ID.

Boot from the VFIO Kernel:

Edit your bootloader configuration for GRUB:

Edit the file: sudo vim /boot/grub/grub.cfg

Then add the following to your "GRUB_CMDLINE" configuration:

amd_iommu=on iommu=pt vfio-pci.ids=your,ids

Then change your configuration:

GRUB_DEFAULT="0" -> 1>2 (replace with your number)

If you're booting from the GRUB menu, you can go under "Advanced options" and see the different kernels. The first option is always 0, the second is 1, and so on. You want to change it to the linux-vfio kernel.
To boot from the "Advanced options," use GRUB_DEFAULT="1>2" with the extra > sign to select the correct kernel (replace 2 with the correct boot option).

For GRUB, run:

sudo grub-mkconfig -o /boot/grub/grub.cfg

Edit your bootloader configuration for Systemd:

Edit the file: sudo vim /boot/loader/entries/arch.conf

Add after the "rw":

amd_iommu=on iommu=pt vfio-pci.ids=your,ids

Then change the bootloader configuration to (DO NOT REMOVE ANYTHING):

linux /vmlinuz-linux-vfio
initrd /initramfs-linux-vfio.img

*You can replace amd_iommu=on with intel_iommu=on if you have an Intel CPU.*
*Replace your,ids with the IDs you saved earlier.*

Create and Edit the Modprobe Config File:

sudo touch /etc/modprobe.d/vfio.conf
sudo vim /etc/modprobe.d/vfio.conf

Paste the following into the file:

options vfio-pci ids=your,ids
softdep nvidia pre: vfio-pci

Replace your,ids with your GPU IDs.

Update the Initramfs:

sudo mkinitcpio -P linux-vfio

Reboot Your System:

sudo reboot now

Load vfio-pci modules:

sudo modprobe vfio-pci

Add the GPU to Your VM in KVM:

In your VM settings, click "Add" and select your NVIDIA GPU and NVIDIA audio device.

MAKE SURE TO USE THE CORRECT HDMI PORT CONNECTED TO YOUR MOTHERBOARD WHEN YOU PASSTHROUGH YOUR DEDICATED GPU TO A VM IF YOU ONLY HAVE ONE DEDICATED GPU AND AN iGPU YOU CAN USE.