(1) GPU and NVAPI are correct — this is not a GPU-detection problem:

info:nvapi64:DXVK-NVAPI v0.9.2 NVAPI gcc 14.0.0 x86_64 plain (witcher3.exe)
info:nvapi64:<-NvAPI_Initialize: OK
info:nvapi64:NvAPI Device: NVIDIA GeForce RTX 3080 10GB (610.57.4)
info:nvapi64:<-NvAPI_SYS_GetDriverAndBranchVersion: OK

(2) Only sl.interposer.dll is loaded. NONE of the Streamline plugin DLLs are ever loaded, although they exist on disk next to the interposer (The Witcher 3/bin/x64_dx12/) and are valid x86-64 PE DLLs:

Loaded L"S:\\steamapps\\common\\The Witcher 3\\bin\\x64_dx12\\sl.interposer.dll"

A grep over the complete +loaddll stream for the plugin DLLs returns zero hits:

grep -c 'Loaded L".*sl\.\(common\|dlss\|reflex\|pcl\)' steam-292030.log   ->   0

Present on disk but never loaded: sl.common.dll, sl.dlss.dll, sl.dlss_d.dll, sl.dlss_g.dll, sl.reflex.dll, sl.pcl.dll.

(3) Streamline reports the failure itself:

[streamline][error]sl.cpp:168[slValidateState] SL not initialized or no plugins found - please make sure to include all required plugins including sl.common

(4) slInit() is never called by the game. Proven by enabling Streamline's own environment-variable logging overrides (SL_ENABLE_CONSOLE_LOGGING=1, SL_LOG_LEVEL=10, SL_LOG_PATH=C:/sldbg). Streamline emits SL_LOG_HINT("Overriding logging settings from environment variables") from inside slInit(). That message never appears in the log, and C:\sldbg\sl.log is never created. The slInit() warnings ("Seems like some DX/VK APIs were invoked before slInit()!!!" and "slInit must be called before any DXGI/D3D12/D3D11/Vulkan APIs are invoked") never appear either.

The game creates the D3D12 device at ~0.5 s and then queries Streamline feature support without ever having initialized Streamline, so it receives eErrorNotInitialized for every feature and greys out all DLSS options.

Analysis

From the upstream NVIDIA Streamline SDK source:

• slValidateState() (source/core/sl.api/sl.cpp) returns eErrorNotInitialized when plugin_manager::arePluginsLoaded() is false.
• arePluginsLoaded() is s_status == ePluginsLoaded || s_status == ePluginsInitialized (source/core/sl.plugin-manager/pluginManager.cpp), and s_status is set to ePluginsLoaded inside loadPlugins() — very early, before plugin enumeration. So if loadPlugins() had run even once, the validation would already pass. The observed failure means loadPlugins() never ran.
• loadPlugins() is called from exactly one place: slInit() (return manager->loadPlugins();), and only when interposer::isEnabled() is true.
• Conclusion: the game never calls slInit() in this environment.

The binary does use the Streamline feature-query API (GetIsDLSSSupported, GetDLSSGSupported, GetDLSSRRSupported are visible in witcher3.exe), so the integration is present — it simply never gets initialized.

One plausible trigger for the game's internal "DLSS not available" gate: the game issues four NVAPI queries whose entry points dxvk-nvapi does not implement, and gets NULL back:

info:nvapi64:nvapi_QueryInterface (0xad298d3f): Unknown function ID
info:nvapi64:nvapi_QueryInterface (0x33c7358c): Unknown function ID
info:nvapi64:nvapi_QueryInterface (0x593e8644): Unknown function ID
info:nvapi64:nvapi_QueryInterface (0xd7c61344): Unknown function ID

It is likely the game treats at least one of these as a hard capability check and disables the entire DLSS/Streamline path rather than falling back. If these entry points can be identified and implemented (or stubbed), that would probably resolve the issue.

Additional information

• The game ships DLSS 4.x (nvngx_dlss.dll carries the NGX rel_310_9 / juicy_penguin weights), i.e. this is the August 2026 "Remastered" release that added Path Tracing, DLSS 4.5, FSR 4 and XeSS 2. The integration may simply be newer than what Wine has been validated against.
• Driver-side NGX is present and correct: /usr/lib/libnvidia-ngx.so.610.57.04, /usr/lib/nvidia/wine/{_nvngx,nvngx,nvngx_dlssg}.dll, and the prefix has _nvngx.dll + nvngx.dll in system32.
• Non-NVIDIA upscalers do work: the log shows amd_fidelityfx_upscaler_dx12.dll, amd_fidelityfx_loader_dx12.dll, libxess.dll and libxess_fg.dll all loading successfully. FSR / XeSS are the practical workaround meanwhile.
• Ray tracing itself is functional with VKD3D_CONFIG=extra_rtas_sync on driver 610 (per https://forums.developer.nvidia.com/t/solution-for-witcher-3-with-rt-under-610-drivers/378760).
• sl.interposer.json cannot be used as an override here: the string table of sl.interposer.dll shows the JSON-config code path is compiled out (production build), so enableInterposer / pathToPlugins cannot be set externally.