GPU Passthough Issues

[apparatus]

You GPU consist of two devices: 0000:03:00.0 video device and 0000:03:00.1 audio device.
You need to hide them both from dom0 as described in the guide:

Create a Gaming HVM

Hardware To have an ‘HVM’ for gaming, you must have A dedicated GPU. By dedicated, it means: it is a secondary GPU, not the GPU used to display dom0. In 2023, ‘Nvidia’ and ‘Amd’ GPU work. Not tested with Intel GPUs. External GPU using thunderbolt work (Create a Gaming HVM - #8 by solene) A screen available for the gaming ‘HVM’. (It can be a physical monitor or just to have multiple cables connected to the screen and switching between input source) Dedicated gaming mouse and keyboard. …

GRUB_CMDLINE_LINUX="... rd.qubes.hide_pci=03:00.0,03:00.1 "