I don't know how many people are in the same situation as me, but for various reasons I currently don't have access to a powerful gaming PC or console, so my Steam Deck LCD is basically my only option for playing games.
When I first tried to run ACE COMBAT 8: WINGS OF THEVE on my Steam Deck LCD, the game itself could launch and I could reach the main menu, but starting Campaign would always crash during mission loading.
After a lot of testing, I finally managed to get past the loading screen, enter an actual Campaign mission, and fly the aircraft.
So I'm sharing the exact configuration that worked for me in case anyone else is stuck at the same point.
My system and final working configuration
- Device: Steam Deck LCD
- SteamOS: 3.8.82 Stable
- Compatibility tool: Proton Experimental
- Swap: 16 GB
- BIOS UMA Frame Buffer Size: 4 GB
- Result: Campaign successfully loads and is actually playable
- Performance: roughly 17–30 FPS depending on the scene
The most important part of my testing was this:
4 GB UMA only → Campaign still crashed.
4 GB UMA + 16 GB Swap → Campaign finally loaded and became playable.
That distinction is important because I had already seen people recommending “just set VRAM to 4 GB,” but that alone did not solve the crash on my LCD Deck.
Why I think memory pressure is involved
The Steam Deck has 16 GB of unified memory, which means the CPU and GPU share the same physical memory pool.
ACE COMBAT 8 is a demanding new game, and in my case simply increasing the UMA reservation to 4 GB was not enough. The game would still crash when loading Campaign.
After adding a 16 GB swap file, the game finally managed to get through the mission loading process.
Obviously, swap is not the same thing as adding another 16 GB of physical RAM. It uses storage as slower backup memory.
My assumption is that this gives the system additional breathing room when RAM pressure becomes too high, instead of the game immediately failing when memory is exhausted.
So, based on my own testing:
The Steam Deck seems physically capable of running AC8, but its limited 16 GB unified memory can become a serious bottleneck during mission loading.

I have not confirmed the exact cause through logs, so treat this as an observation from testing rather than a proven technical diagnosis.
Step 1: Use Proton Experimental
In Steam:
ACE COMBAT 8 → Properties → Compatibility
Enable:
Force the use of a specific Steam Play compatibility tool
Then select:
Proton Experimental
This is the compatibility layer I was using when Campaign finally worked.
I did not need SteamOS Beta or Preview. My successful test was done on:
SteamOS 3.8.82 Stable
Step 2: Set up 16 GB Swap with CryoUtilities
I followed this Bilibili tutorial by 金喘喘:
修改SteamDeck虚拟内存、显存，减少游戏卡顿！保姆级教程！
Full link:
https://www.bilibili.com/video/BV1psFYzLE85
The process shown in the video is roughly:
1. Switch the Steam Deck to Desktop Mode.
2. Install/open CryoUtilities.
3. If required, set a local Linux user password first.
- This is not your Steam account password.
- It is the password for the local deck user.
4. In CryoUtilities, open the Home page and apply Recommended settings.
5. Open the Swap section and confirm:
- Current Swap Size: 16 GB
- Current Swappiness: 1
6. Check the Memory page and make sure the recommended settings have been applied.
Important:
CryoUtilities' Recommended button changes more than just swap size. It may also modify HugePages and other memory-related settings.
So I cannot say that this is a scientifically isolated test of:
“16 GB Swap alone fixes AC8.”

What I can say is:
The CryoUtilities recommended memory configuration, including 16 GB Swap, combined with 4 GB UMA and Proton Experimental, worked on my Steam Deck LCD.

Also remember that a 16 GB swap file consumes around 16 GB of storage space.
Do not fill your system drive completely.
Step 3: Set UMA Frame Buffer Size to 4 GB
This setting has to be changed in the Steam Deck BIOS.
1. Fully shut down the Steam Deck.
2. Hold Volume Up (+).
3. Press the Power button once.
4. After the startup sound, release the buttons and wait for the boot menu.
5. Select:
Setup Utility → Advanced
6. Find:
UMA Frame Buffer Size
7. Change it to:
4G
8. Save and exit.
9. Boot back into SteamOS.
You can then reopen CryoUtilities and check the VRAM section to confirm that it reports 4 GB.
Again:
4 GB UMA by itself did NOT fix the Campaign crash on my Deck.
I tested that first, and Campaign still crashed.
The game only started working after I also configured the 16 GB swap setup.
Actual performance after Campaign started working
Once everything was configured, I was finally able to get past the exact Campaign loading point that previously crashed every time.
I entered the mission and could actually control the aircraft.
Performance on my Steam Deck LCD is roughly:
- High altitude / fewer objects on screen: often around 25–27 FPS
- Normal gameplay: generally in the low-to-mid 20s
- Close to the ground / more geometry / some first-person scenes: can drop to around 17 FPS
- Best case: close to 30 FPS
So this is not a locked 30 FPS experience.
But for me, 17–30 FPS is still better than not being able to play Campaign at all.
The purpose of this post is mainly to document how I got the Campaign to load, not to claim that AC8 runs perfectly on Steam Deck.
About ray tracing and Steam Deck performance
AC8 has unusually heavy GPU requirements.
The official minimum GPU class includes cards such as the RTX 2060 and RX 6600 XT, while the Steam Deck GPU is a much smaller 8-CU RDNA2 design.
The RTX 2060 has 30 RT Cores, the RX 6600 XT has 32 RDNA2 Compute Units with Ray Accelerators, while the Steam Deck only has 8 RDNA2 Compute Units.
However, these different ray-tracing architectures are not directly comparable one-to-one, so I would not say that “the Deck is slow simply because it only has eight RT units.”
The more general conclusion is simply:
AC8 is asking a lot from a 15 W handheld APU, especially if the game relies heavily on modern UE5 rendering features and ray tracing-related workloads.

That is probably one of the reasons why the game spends so much time in the 17–30 FPS range even after the crash is solved.
Important: Denuvo / CodeFusion activation limit
During all of this testing, I repeatedly changed Proton versions and system/memory settings within a short period of time.
Eventually I got a CodeFusion / Denuvo activation error instead of the normal AMD warning.

In my case, this was temporary.
This is important because it can look like your new configuration broke the game.
It probably did not.
Denuvo can treat major compatibility-layer or system-environment changes as a new activation environment. If you switch between Proton versions and configurations too many times within a short period, you may hit an activation limit.
If this happens, the safest thing to do is:
Stop changing Proton/system settings and wait before trying again.
In my case, after the activation issue cleared, the game launched successfully with the working configuration.
So I strongly recommend:
Once you find a configuration you want to test, keep it unchanged instead of rapidly switching between multiple Proton versions.

Final working configuration / TL;DR
Steam Deck LCD
SteamOS 3.8.82 Stable
Proton Experimental
UMA Frame Buffer Size: 4 GB
CryoUtilities recommended memory settings
Swap: 16 GB
Swappiness: 1
Result:
Campaign successfully loads and is playable at roughly 17–30 FPS.
Most importantly:
4 GB UMA alone still crashed for me.
After adding the 16 GB swap configuration, Campaign finally worked.

I cannot guarantee that every Steam Deck will behave the same way, and I haven't isolated every individual CryoUtilities setting.
But if your AC8 can reach the menu and then crashes specifically while loading Campaign, this configuration may be worth trying.
If anyone gets different results on LCD / OLED / different SteamOS versions / different Proton builds, please post your configuration below. It would be useful to figure out which parts of this setup are actually required.