SteamOS Not Installing on my PC

SteamOS installer black screens after boot on desktop PC (RX 5600 XT)

I'm trying to install SteamOS on my desktop PC using the official SteamOS image from Valve's website, but I can't get past the initial boot process.

The USB boots correctly and I get the terminal output showing SteamOS starting up. It goes through a bunch of services and everything shows [ OK ], but after that it switches to a black screen with a solid _ cursor in the top-left corner and stays there indefinitely.

I left it on this screen for over an hour and nothing changed.

Hardware:
CPU: Ryzen 5 5500
GPU: Radeon RX 5600 XT
RAM: 16GB DDR4
Motherboard: Gigabyte B450M DS3H WiFi
Displays:
1440p 360Hz OLED (DisplayPort)
1080p 165Hz TN (DisplayPort)
SteamOS image:

steamdeck-oobe-repair-20260707.10-3.8.14.img

Flashed using Rufus 4.15.

BIOS settings:
CSM: Disabled
Secure Boot: Disabled
Fast Boot: Disabled
What I tried:
Booting both UEFI entries created by Rufus (Partition 1 and Partition 2)
Using both monitors individually
Leaving it on the black screen for over an hour
Recreating the USB installer
Other details:
The PC does not appear completely frozen. Caps Lock still works.
The USB drive activity light continues blinking for a while after the screen goes black.
One time the mouse cursor appeared and was movable, but the SteamOS interface never loaded.

The payload names no repository file, test, or code entry point. Start by reproducing the black-screen boot with the listed SteamOS image and RX 5600 XT setup; done would require identifying a confirmed fix or actionable scope.