(This fix was originally by Mominjo on ProtonDB for WRC 9 FIA World Rally Championship, another game using the KT Engine. Tried it on RimS and worked like a charm!)

Going into Desktop Mode on the Steam Deck. Using Protontricks (please install from app discovery in desktop mode, search 'protontricks'. Look up about Protontricks on Steam Deck if still unsure). This is to change the Windows version to Windows 7. Adding a Launch Command in the game prop

After installing RiMs Racing, go into Desktop Mode .

Open Protontricks , select RiMs Racing then OK .

(After a few moments), select select the default wineprefix then OK .

Now select Run winecfg then OK .

We are now in the Wine Configuration window for RiMs Racing and should be in the Application tab (select it if not).

At the bottom, change windows versions to Windows 7 then Apply .

Now find RiMs racing in your Steam Library, click Manage , then Properties .

Scroll down to Launch Options , then post the below command into the box.