In order for you to play X4: Foundations on Linux with minimal graphics settings, your computer must meet the following requirements
Operating System:
SteamOS (64-bit) or Ubuntu 18.04 (64-bit)
Processor (CPU):
Intel i5-4590 3.3GHz or AMD equivalent
Memory (RAM):
8 GB RAM
Graphics Card:
Nvidia GTX 780/970 or AMD equivalent (Vulkan support required)
Storage:
35 GB available space
In order to play X4: Foundations on Linux with maximum graphics settings, you need a computer with a configuration no worse than the following
Operating System:
SteamOS (64-bit) or Ubuntu 18.04 (64-bit)
Processor (CPU):
Intel Core i7-6700 or AMD equivalent
Memory (RAM):
16 GB RAM
Graphics Card:
Nvidia GTX 1070 or AMD equivalent (Vulkan support required)
Storage:
50 GB available space