Ensure you have applied the 4GB Patch to your Omsi.exe . Additionally, reduce your AI traffic density, reduce texture resolution, and lower your object draw distance in the OMSI 2 graphics options menu.

Before changing game files, navigate to your root folder: ...\Steam\steamapps\common\OMSI 2\ Copy your Sceneryobjects and Splines folders to a safe location. If an addon overwrites a file and breaks another map, restoration is easy. 3. Merge the Folders

You can find these maps and related mods on dedicated Polish community forums and simulation databases: Strefa OMSI

: This means you are missing required splines or textures. Double-check the download page to ensure you did not miss a secondary "Asset Pack" link.