Couch Lag

Steam Deck and Moonlight: fixing a black screen

Short answer: First decide which side the Deck is on. If the Deck runs Moonlight (the client), a black stream almost always comes from the PC; use the black-screen checks for the host. If the Deck runs Sunshine in Game Mode (the host), there is an open Sunshine issue where the picture goes black, with audio, once a game starts. A community workaround sets GAMESCOPE_COMPOSITE_FORCE to 1 before you connect.

Checked October 30, 2026 against Moonlight PC v6.2.0 and Sunshine v2026.914.233613 (latest stable releases) and their documentation. Sources are listed at the end of the page.

If the Deck is the client (Moonlight on the Deck)

  • Black video, but you hear the game: the PC isn’t capturing. Work through the black screen with audio checks on the host: a display that’s on, the right GPU, the Desktop app test.
  • Moonlight won’t start in Game Mode: in July 2026, a Mesa update made the Moonlight Flatpak crash on launch in Game Mode (Moonlight issue #1930). Flathub shipped a fix on July 18, 2026 (PR #83) that keeps HDR working. Update Moonlight from Discover. The version number didn’t change, because only bundled libraries were updated. People used a launch option, ENABLE_GAMESCOPE_WSI=0 %command%, as a stopgap, but it was reported to break HDR, so remove it once you’re updated.
  • Settings: the Deck’s screen is 1280×800. Moonlight PC’s default bitrate there is about 11 Mbps at 60 fps (see the bitrate table).

If the Deck is the host (Sunshine on SteamOS)

Sunshine issue #5839, which is still open, reports black video with working audio in some Game Mode streams with KMS capture since Sunshine 2026.906. Other reporters see the same thing on SteamOS desktops, Bazzite and a ROG Ally. Streams of Steam’s menus can work, then go black once a game starts.

Community workaround (not an official fix): several reporters say that setting Gamescope’s composite-force property to 1 before Moonlight connects brings the picture back:

DISPLAY=:0 xprop -root -f GAMESCOPE_COMPOSITE_FORCE 32c -set GAMESCOPE_COMPOSITE_FORCE 1

Some people run it as a prep command so it applies to every stream. Treat it as temporary, and check the issue for an official fix before relying on it.

  • Sunshine’s docs say KMS capture needs the native package and won’t work from Flatpak or AppImage, because those can’t get the privileges it needs. XDG Portal capture works with every package type.

If the Deck runs Windows and Sunshine

A Sunshine contributor explained (issue #1514) that Windows on the Deck needs a virtual monitor or an HDMI dummy plug for Sunshine to capture, because of a Windows capture-API limitation. See streaming without a dummy plug.

FAQ

Why is my Moonlight stream black on the Steam Deck?

If the Deck is the client, the host PC usually isn’t capturing video: check the PC’s display, GPU and the Desktop app. If the Deck is a Sunshine host in Game Mode, see the open Sunshine issue #5839 and its community workaround.

Moonlight stopped launching in Steam Deck Game Mode. What happened?

A July 2026 Mesa update caused the Moonlight Flatpak to crash in Game Mode. Flathub shipped a fix on July 18, 2026; update Moonlight from Discover and remove any ENABLE_GAMESCOPE_WSI=0 launch option.

What resolution should I stream to a Steam Deck?

The Deck’s screen is 1280×800, so streaming higher costs bandwidth without a sharper picture. Moonlight PC’s default bitrate at 1280×800 and 60 fps is about 11 Mbps.

Sources

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