Sorry for the late reply, didn’t feel like doing anything the previous days. I just finished testing / working around / making libvirt able to detect OVMF/UEFI. Took me around 2 hours or so (researching, testing and documenting it altogether, I should probably do a Wiki post/entry on L1 Forum, but fugg me, I’m too lazy). Here we go:
So, first things first:
sudo xbps-install -S libvirt qemu virt-manager virt-manager-tools
If you have libvirtd and virtlogd running, kill them:
sudo sv d libvirtd
sudo sv d virtlogd
(inserting random emoji to make this wall-of-text more readable)

According to those steps here: https://github.com/tianocore/tianocore.github.io/wiki/How-to-run-OVMF , we should download 3 1 rpm packages from under jenkins/edk2 and decrompress them it:
(apparently, you only need the edk2.git-ovmf package - MAKE SURE YOU DOWNLOAD IT FOR YOUR ARCHITECTURE, though since you are running a 3900X, I doubt you are running anything except Void x86_64-gcc/musl)
Fortunately, there is a script in the Void repo which helps us do just that:
sudo xbps-install -S rpmextract
rpmextract edk2.git-ovmf-x64-0-20201222.1538.g014b9850f2.noarch.rpm
Make sure it extracted correctly (note: you should still be in your home or Downloads folder, wherever you got the rpm)
ls -alh usr/share/edk2.git/ovmf-x64/
Verify this image can be used:
qemu-system-x86_64 -bios usr/share/edk2.git/ovmf-x64/OVMF-pure-efi.fd
You should be seeing a Tianocore boot screen and maybe it trying a PXE boot. Exit this screen and rename the folders:
mv usr/share/edk2.git/ usr/share/ovmf
mv usr/share/ovmf/ovmf-x64 usr/share/ovmf/x64
Copy some files around
cp usr/share/ovmf/x64/OVMF_CODE-pure-efi.fd usr/share/ovmf/x64/OVMF_CODE.fd
cp usr/share/ovmf/x64/OVMF_VARS-pure-efi.fd usr/share/ovmf/x64/OVMF_VARS.fd
cp usr/share/ovmf/x64/OVMF-pure-efi.fd usr/share/ovmf/x64/OVMF.fd

Copy the folder in /usr/share
sudo cp -r usr/share/ovmf /usr/share/
Create /etc/qemu/firmware
sudo mkdir -p /etc/qemu/firmware
Add this config in /etc/qemu/firmware/60-ovmf-x86_64.json:
60-ovmf-x86_64.json
{
"description": "UEFI OVMF firmware for x86_64",
"interface-types": [
"uefi"
],
"mapping": {
"device": "flash",
"executable": {
"filename": "/usr/share/ovmf/x64/OVMF_CODE.fd",
"format": "raw"
},
"nvram-template": {
"filename": "/usr/share/ovmf/x64/OVMF_VARS.fd",
"format": "raw"
}
},
"targets": [
{
"architecture": "x86_64",
"machines": [
"pc-i440fx-*",
"pc-q35-*"
]
}
],
"features": [
"acpi-s3",
"amd-sev",
"verbose-dynamic"
],
"tags": [
]
}
Enable libvirtd and virtlogd:
sudo ln -s /etc/sv/libvirtd /etc/runit/runsvdir/default/
sudo ln -s /etc/sv/virtlogd /etc/runit/runsvdir/default/
If you had those already, start them daemons you killed at the begining:
sudo sv u libvirtd
sudo sv u virtlogd
Make sure they are up:
sudo sv status libvirtd
sudo sv status virtlogd
Add your user to libvirt group:
sudo usermod -a -G libvirt {ur username}
bro ehm… sibling*
Virt-Manager should now detect UEFI/OVMF now when creating a new VM with custom config, or when editing existing VM config. This has been tested on an ASRock J3455M running a void-x86_64-musl build. I created a generic OS VM (custom settings) with q35 and UEFI, added a virtual CD-ROM and booted into an alpine-linux iso. Worked fine for the 20 seconds I tested it. Hope I have not missed any steps.
If I made grammar errors, well, I’m too lazy to look through this tutorial again. In any case, I hope this works, I like helping the few Void users on this forum however I can (I am a noob myself, but I am proud of my web searching skills).