CesiumIonClient.lib(Connection.obj) : error LNK2019: unresolved external symbol _Thrd_sleep_for referenced in function “void __cdecl std::this_thread::sleep_for<__int64,struct std::ratio<1,1000> >(class std::chrono::duration<__int64,struct std::ratio<1,1000> > const &)” (??$sleep_for@_JU?$ratio@$00$0DOI@@std@@@this_thread@std@@YAXAEBV?$duration@_JU?$ratio@$00$0DOI@@std@@@chrono@1@@Z)
I just happened to run into this myself. In my case, it was caused by having the “MSVC v143 - VS2022 C++ x64/x86 build tools (v14.34-17.4)” component of Visual Studio 2022 installed. When this particular version of MSVC is installed, Unreal will use it. When you build cesium-native, though, cmake will usually pick the latest version of MSVC available. That meant I was building Cesium Native with MSVC v14.40, and attempting to link with v14.34, which is not a valid thing to do.
You can fix this by either uninstalling the extraneous version of MSVC, or by telling cmake to use it. You can do the latter by adding -DCMAKE_GENERATOR_TOOLSET="version=14.34" to the cmake configure command line when building Cesium Native.