You two are not the only ones. I upgraded to 6.9 and the VM was working fine. I upgraded my hardware from Intel to AMD a few days later, I'm in the same boat you two are now. Rolling back to try 6.8.3 now...
Intel 6700k
ASUS Maximus Hero VIII
upgraded to:
Ryzen 7 3700x
ASUS Prime X570-Pro
GPU is an ASUS GTX 1060.
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Edit:
I resolved my issue. Having dug deeper I found the following in my VM Log:
2021-03-06T06:32:32.186442Z qemu-system-x86_64: vfio_region_write(0000:09:00.0:region1+0x1be6ba, 0x0,1) failed: Device or resource busy
Some searching yielded another thread:
Adding a user script to User Script Plugin that runs when the array starts seems to have solved my issue, I was able to successfully boot into Windows 10 VM with the GTX 1060 passed through. I have installed the drivers successfully.
The script:
#!/bin/bash
echo 0 > /sys/class/vtconsole/vtcon0/bind
echo 0 > /sys/class/vtconsole/vtcon1/bind
echo efi-framebuffer.0 > /sys/bus/platform/drivers/efi-framebuffer/unbind
Edit 2:
For clarification, my VM would not load on 6.8.3 or 6.9.0 with GTX 1060 as my primary and only gpu in the system. This script fixed the problem for me in both 6.8.3 and 6.9.0.