Editing Openai/69492970-fd84-8012-81ad-fad51507b9fe (section)

=== Assistant: YES — that helps a lot. ===
YES — that helps a lot. This actually nails the root cause.
You’ve basically described a known SteamOS Game Mode limitation/bug, not a broken eGPU.

Let me summarize what’s happening in plain terms, then give you the correct fix (and the limits you can’t bypass).

==== What your new info confirms (this is the key) ====
* ✅ Desktop Mode - eGPU is detected - HDMI on the eGPU works - Display shows on the TV
* ❌ Game Mode - Boots fine - Does not see or use the eGPU - HDMI on the eGPU stays black

👉 This means:

: Your eGPU is working perfectly — Game Mode just isn’t initializing it.

This is not Thunderbolt, not BIOS, not drivers missing.

==== Why this happens (important) ====

===== SteamOS has two completely different graphics stacks: =====

===== Desktop Mode =====
* KDE Plasma
* Normal Linux DRM/KMS
* xrandr, multiple GPUs, external displays
* eGPU works 👍

===== Game Mode =====
* Gamescope
* Wayland-only
* Single-GPU–first design
* Aggressively locks onto the iGPU
* Very limited multi-GPU / eGPU display support

Right now, Gamescope often treats AMD eGPUs as “render-only” or ignores them entirely, especially for external displays.

That’s why:
* Desktop Mode = fine
* Game Mode = nope

You didn’t do anything wrong.

==== The critical thing to understand (no sugarcoating) ====

: SteamOS Game Mode does NOT reliably support AMD eGPUs driving external displays.

Sometimes it works.
Updates break it.
Valve fixes it.
Next update breaks it again.

What you’re seeing is a regression in Game Mode, not Desktop Mode.

==== What does work (reliable paths) ====

===== ✅ OPTION 1 (Most reliable): Use Desktop Mode for TV gaming =====

This is what many eGPU users end up doing.
* Stay in Desktop Mode
* Launch Steam from there
* Use Big Picture if you want the console feel
* HDMI + eGPU works consistently

This avoids Gamescope entirely.

===== ✅ OPTION 2: Force Game Mode to “see” the external display (sometimes works) =====

This is the only semi-reliable trick:
# Boot into Desktop Mode
# Make the TV the primary display ``<code>bash xrandr --output HDMI-1 --primary <syntaxhighlight>3. Disable the internal display (optional but helps) </syntaxhighlight>bash xrandr --output eDP-1 --off <syntaxhighlight>4. Without rebooting, switch to Game Mode

If you’re lucky:
* Game Mode will inherit the display state
* HDMI will work

If you reboot after this, it usually breaks again.

===== ✅ OPTION 3: Force eGPU rendering per-game (render only) =====

Even if HDMI doesn’t light up, you can still make games render on the eGPU (internal screen only):

Steam launch options:

</syntaxhighlight>bash
DRI_PRIME=1 %command%

</code>``

This does not fix HDMI output, but confirms the GPU is usable.

==== What does NOT work (so you don’t waste time) ====
* ❌ BIOS changes
* ❌ GRUB “primary GPU” hacks
* ❌ Disabling the iGPU
* ❌ Wayland tweaks inside Game Mode
* ❌ Reinstalling SteamOS

Game Mode is hard-coded around Gamescope behavior.

==== The honest current state (as of now) ====
* Desktop Mode + eGPU + HDMI → ✅ supported
* Game Mode + AMD eGPU + HDMI → ❌ unreliable / broken
* NVIDIA eGPU → works more often (sad but true)
* Internal screen + eGPU rendering → ✅

This matches exactly what you’re seeing.

==== My recommendation (real talk) ====

If your goal is TV + couch gaming with an eGPU:

👉 Use Desktop Mode + Steam Big Picture

If your goal is handheld + dock switching:

👉 eGPU on SteamOS is still rough, especially in Game Mode.

==== If you want, I can: ====
* Help you make Desktop Mode boot straight into Steam Big Picture
* Show how to make it feel identical to Game Mode
* Track the exact SteamOS update where this regressed
* Give you a “least pain” setup for your use case

Just tell me how you want to use it day-to-day, and I’ll tailor the setup 👌