I guess I should have quoted the error message from KSP about needing libc++abi1-8 & libc++1-8. When I checked and had libc++1-11, libc++abi1-11. I figured the Error message in the gui was old. And a later version was required.
KSP.log
EXC 21:02:05.454] DllNotFoundException: principia
principia.ksp_plugin_adapter.Log.InitGoogleLogging () (at <b7045db6431e4c8ca505f0d40f37267d>:0)
principia.ksp_plugin_adapter.Loader.LoadPrincipiaDllAndInitGoogleLogging () (at <b7045db6431e4c8ca505f0d40f37267d>:0)
UnityEngine.DebugLogHandler:LogException(Exception, Object)
ModuleManager.UnityLogHandle.InterceptLogHandler:LogException(Exception, Object)
UnityEngine.Debug:LogException(Exception)
principia.ksp_plugin_adapter.Loader:LoadPrincipiaDllAndInitGoogleLogging()
principia.ksp_plugin_adapter.PrincipiaPluginAdapter:.ctor()
UnityEngine.GameObject:AddComponent(Type)
ScenarioRunner:AddModule(String)
ScenarioRunner:AddModule(ConfigNode)
ProtoScenarioModule:Load(ScenarioRunner)
ScenarioRunner:LoadModules(List`1)
ScenarioRunner:AddMainMenuScenarios()
ScenarioRunner:onLevelWasLoaded(GameScenes)
EventData`1:Fire(GameScenes)
<FireLoadedEvent>d__46:MoveNext()
UnityEngine.SetupCoroutine:InvokeMoveNext(IEnumerator, IntPtr)
[ERR 21:02:05.455] The Principia DLL failed to load.
An unknown error occurred; detected OS Unix 4.19.0.0 64-bit; tried loading dll at 'GameData/Principia/Linux64/principia.so', 'GameData/Principia/MacOS64/principia.so'. Note that libc++abi1-8 and libc++1-8 or later (Linux) or Sierra or later (MacOS) are required.
Warning: don't load a Principia save before you have fixed this error; it might get damaged.
Thank You,
Ned