Hi @Liam Graham ,
Thank you for bringing up this question. For the public GDK on Windows PC, I could not find a documented location for xgameplatform.lib. The GDKX library layout lists it as a core dependency for Xbox console builds, but not for the desktop build. The project configuration guidance likewise includes it in the Xbox library set and points the Xbox build to GXDK library directories.
Your expectation is understandable as the SDK and tools requirements page says xgameplatform.lib is part of the Windows SDK. That wording does not appear to line up with the platform-specific build guidance or with what you found in your installation. I cannot confirm from those documents that it is supplied in the public Windows SDK.
For a PC GDK build, xgameruntime.lib is the documented library for Gaming Runtime APIs, alongside the Windows libraries required by the other APIs you use. There is no need to add OneCore.lib simply to replace a missing xgameplatform.lib. The GDK introduction describes linking xgameplatform.lib when building for Xbox to restrict links to Game OS-supported APIs.
If this instruction is applicable to your situation, I would greatly appreciate it if you could follow the instruction here so others experiencing similar behavior can benefit from it as well.