alt Hacker NewsYes, they are easy to port a lot of the time. Especially now because you can use DXVK to translate DirectX calls into Vulkan, so you don't need to write a Vulkan renderer. Input is sometimes a trickier one to deal with but a lot of the time games are using cross-platform libraries for that already!
Despite all this the Unity engine has spotty Linux support. Some games run better under Wine vs. Unity's native Linux builds. It's Vulkan renderer has had a memory leak for a while now. Input has randomly decided to double keypresses on some distros.
The hard part of Linux ports isn't the first 90% (Using the Linux APIs). It's the second 90%.
Platform bugs, build issues, distro differences, implicitly relying on behavior of Windows. It's not just "use Linux API", there's a lot of effort to ship properly. Lots of effort for a tiny user base. There's more users now, but proton is probably a better target than native Linux for games.