Compatibility Report
Name of the game with compatibility issues: Dark and Darker
Steam AppID of the game: 2016590
System Information
GPU: NVIDIA GeForce RTX 3070 Ti
Video driver version: NVIDIA proprietary 595.84.0
Kernel version: 7.0.0-28-generic (Ubuntu 26)
Link to full system information report as Gist:
Proton version: GE-Proton11-5. Also reproduced on stock Proton Experimental, stock Proton 11.0-100 ("Proton Hotfix"), GE-Proton10-34, and GE-Proton11-1.
I confirm:
that I haven't found an existing compatibility report for this game.
#8208 exists for this AppID but describes a different, older failure mode ("Tavern is not working!" at character select). This report is a distinct failure in the anti-cheat service installer, occurring before the game process starts.
that I have checked whether there are updates for my system available.
Symptoms

The game's Ironshield anti-cheat bootstrapper (Tavern.exe) fails before the game process ever starts. In-game dialog:

An error has occurred. Code 9. Unable to update anti-cheat components. Please restart your PC and relaunch the game.

The Unreal Engine process (DungeonCrawler) never launches, so no game-side log is written.

The game worked under Proton for months prior to this. The failure began after Steam re-acquired the game's depot (recorded in config.vdf as "buildid":0 → "target_buildid":24707614, 2.28 GB of a 3.88 GB install), which forced the anti-cheat to update its components — and therefore to install and reconfigure its Windows service, TavernWorker. That service-configuration path is where it fails.

Root cause visible in the Proton log

The anti-cheat bootstrapper is launched as:

Command: ['.../steamapps/common/Dark and Darker/Tavern.exe',
'-server=http://live-gateway.lunatichigh.net',
'-steam=1', '-taverntype=steam', '-tavernapp=dad']

The following block repeats four times, after which the process gives up and reports code 9:

7099.456:0030:019c:fixme:service:svcctl_ChangeServiceConfigW Setting password not supported
7099.456:01a0:01a4:fixme:service:SetServiceObjectSecurity 0000000000299B80 5 000000000010BB90
7099.457:0030:019c:fixme:service:svcctl_ChangeServiceConfig2W SERVICE_CONFIG_FAILURE_ACTIONS not implemented: period 0 msg L"" cmd L""
7099.457:0030:019c:fixme:service:svcctl_ChangeServiceConfig2W SERVICE_CONFIG_SERVICE_SID_INFO not implemented: type 0
7099.457:01a0:01a4:err:ole:get_arm_offset_from_union_arm_selector no arm for 0x8 and no default case
7099.457:01a0:01a4:warn:seh:dispatch_exception backtrace: --- Exception 0x6c5.

Exception 0x6c5 is 1733 decimal — RPC_S_INVALID_TAG ("the union tag does not match the value of the discriminant"). The unwind trace following each exception is entirely inside rpcrt4.dll.

Also observed in the same window:

fixme:service:QueryServiceObjectSecurity information 5 not supported
fixme:service:QueryServiceConfig2W Level 6 not implemented
err:service:device_notify_proc failed to get event, error 1726

(1726 = RPC_S_CALL_FAILED.)

Exact root cause: SC_RPC_CONFIG_INFOW has no arm for SERVICE_CONFIG_TRIGGER_INFO

The union selector 0x8 in the error message is dwInfoLevel == 8, i.e. SERVICE_CONFIG_TRIGGER_INFO.

Wine's SC_RPC_CONFIG_INFOW union in include/wine/svcctl.idl defines arms for levels 1–7 only, and has no [default] arm:

c
typedef struct _SC_RPC_CONFIG_INFOW {
DWORD dwInfoLevel;
[switch_is(dwInfoLevel)] union {
[case(SERVICE_CONFIG_DESCRIPTION)] SERVICE_DESCRIPTIONW *descr;
[case(SERVICE_CONFIG_FAILURE_ACTIONS)] SERVICE_FAILURE_ACTIONSW *actions;
[case(SERVICE_CONFIG_DELAYED_AUTO_START_INFO)] SERVICE_DELAYED_AUTO_START_INFO *delayedstart;
[case(SERVICE_CONFIG_FAILURE_ACTIONS_FLAG)] SERVICE_FAILURE_ACTIONS_FLAG *actionsflag;
[case(SERVICE_CONFIG_SERVICE_SID_INFO)] SERVICE_SID_INFO *sid;
[case(SERVICE_CONFIG_REQUIRED_PRIVILEGES_INFO)] SERVICE_RPC_REQUIRED_PRIVILEGES_INFO *privinfo;
[case(SERVICE_CONFIG_PRESHUTDOWN_INFO)] SERVICE_PRESHUTDOWN_INFO *preshutdown;
};
} SC_RPC_CONFIG_INFOW;

SERVICE_CONFIG_TRIGGER_INFO (8), SERVICE_CONFIG_PREFERRED_NODE (9) and SERVICE_CONFIG_LAUNCH_PROTECTED (12) are all absent. Because there is no [default] arm either, the NDR marshaller raises RPC_S_INVALID_TAG as a structured exception rather than returning an error code — and the anti-cheat treats that as fatal.

Ironshield registers TavernWorker as a trigger-started service, so this call is not optional for it.

Suggested fixes, smallest first:

Add a [default] ; arm to SC_RPC_CONFIG_INFOW so unsupported levels return ERROR_INVALID_LEVEL instead of raising an exception. This alone may be enough to unblock callers that tolerate a failed trigger-config call.
Implement SERVICE_CONFIG_TRIGGER_INFO properly — add SERVICE_TRIGGER_INFO / SERVICE_TRIGGER / SERVICE_TRIGGER_SPECIFIC_DATA_ITEM to the IDL and handle level 8 in programs/services/.
Other unimplemented SCM functionality hit in the same sequence
SetServiceObjectSecurity / QueryServiceObjectSecurity with SECURITY_INFORMATION = 5 (OWNER | DACL)
ChangeServiceConfig2W / QueryServiceConfig2W level 6 — SERVICE_CONFIG_REQUIRED_PRIVILEGES_INFO
ChangeServiceConfig2W level 2 — SERVICE_CONFIG_FAILURE_ACTIONS
ChangeServiceConfig2W level 5 — SERVICE_CONFIG_SERVICE_SID_INFO
ChangeServiceConfigW with a service account password

Note that these are logged as fixme (non-fatal); only the level-8 union arm raises.

Note on kernel-mode

The game ships a kernel driver (tvk.sys, ~5 MB) alongside the Tavern components, but no attempt to load it appears anywhere in the log. The only ZwLoadDriver call is Wine's own winebth:

err:ntoskrnl:ZwLoadDriver failed to create driver L"\Registry\Machine\System\CurrentControlSet\Services\winebth": c0000142

So this failure does not appear to require kernel-mode support — only the user-mode Service Control Manager paths listed above.

Reproduction
Install Dark and Darker (AppID 2016590) on Linux under Proton.
Put the anti-cheat in a state where it must update its components and (re)register its service — e.g. use a brand-new Proton prefix, or let Steam re-acquire the game depot.
Launch with empty launch options.
The launcher window appears briefly, then errors with "Code 9 — unable to update anti-cheat components." The game process never starts.

Reproduced on stock Proton Experimental and stock Proton 11.0-100 (Proton Hotfix), as well as GE-Proton11-5 (on a completely fresh prefix), GE-Proton10-34, and GE-Proton11-1. This is not GE-specific.

Ruled out
Filesystem / permissions — library is on ext4 (rw,nosuid,nodev,relatime); the anti-cheat successfully writes its component files (drive_c/ProgramData/Tavern/Tavern_1_1.bin, TavernCommon_1_1.bin) before failing.
Launch options — reproduced with the field completely empty; gamescope and gamemoderun wrappers removed.
protonfixes — confirmed running on GE-Proton11-5 (All checks successful); no protonfix exists for this AppID (No main stage global protonfix found for "Dark and Darker" (2016590)).
Stale prefix — reproduced on a freshly generated prefix.
Leftover anti-cheat processes — pgrep -fa -i tavern empty between attempts.
Duplicate Steam installs — no Flatpak Steam present.
Game install integrity — reproduced after Steam file verification and after a full reinstall.