I'm afraid I did that reinstall run before seeing your reply. I didn't realise there were two debug.err files as there is that one mentioned in my original post that just points to the users file.
Debug Message: Current Time UTC: 08-21-2021 16:33
Debug Message: Version 4.2, Build #10730, last updated on: 08-21-2021 17:16
Debug Message: Product Version 23.1.6.9
Debug Message: Steam Build
Debug Message: Working Directory: K:\SteamLibrary Kingston\steamapps\common\Galactic Civilizations III
Debug Message: Initializing DLC status. Online: 1
Debug Message: DLC0_Founders Owned: 0 Installed 0 PathExists: 0 Enabled By Default 1
Debug Message: DLC1_MapPack Owned: 1 Installed 0 PathExists: 0 Enabled By Default 1
Debug Message: DLC1_5_Registration Owned: 1 Installed 0 PathExists: 0 Enabled By Default 1
Debug Message: DLC2_MegaEvents Owned: 1 Installed 0 PathExists: 0 Enabled By Default 1
Debug Message: DLC3_Snathi Owned: 0 Installed 0 PathExists: 0 Enabled By Default 1
Debug Message: DLC4_PrecursorWorlds Owned: 0 Installed 0 PathExists: 0 Enabled By Default 1
Debug Message: EXP1_Mercenaries Owned: 0 Installed 0 PathExists: 0 Enabled By Default 1
Debug Message: DLC5_BuildersKit Owned: 0 Installed 0 PathExists: 0 Enabled By Default 1
Debug Message: DLC6_RiseoftheTerrans Owned: 0 Installed 0 PathExists: 0 Enabled By Default 1
Debug Message: DLC7_LostTreasures Owned: 0 Installed 0 PathExists: 0 Enabled By Default 1
Debug Message: DLC8_AltarianProphecy Owned: 0 Installed 0 PathExists: 0 Enabled By Default 1
Debug Message: EXP2_Crusade Owned: 1 Installed 0 PathExists: 0 Enabled By Default 1
Debug Message: DLC10_MechKit Owned: 0 Installed 0 PathExists: 0 Enabled By Default 1
Debug Message: EXP3_Intrigue Owned: 0 Installed 0 PathExists: 0 Enabled By Default 1
Debug Message: DLC11_StarControlHeroes Owned: 0 Installed 0 PathExists: 0 Enabled By Default 1
Debug Message: EXP4_Retribution Owned: 1 Installed 0 PathExists: 0 Enabled By Default 1
Debug Message: DLC12_StarControlVillains Owned: 0 Installed 0 PathExists: 0 Enabled By Default 1
Debug Message: DLC14_WorldsInCrisis Owned: 0 Installed 0 PathExists: 0 Enabled By Default 1
Debug Message: Finished initializing DLC status
Debug Message: Personal folder located at C:\Users\Dom\Documents
Debug Message: Personal folder located at C:\Users\Dom\Documents
Debug Message: Initializing data directories
Debug Message: Checking if data bins needs to be rebuilt.
Debug Message: Loading options binary
DebugMessage: Force Clean generated files: 0
Debug Message: Attempting to login using persistent auth.
Debug Message: No existing persistent auth credentials were found for automatic login.
Debug Message: [EOS SDK] Login Failed - Error Code: EOS_InvalidAuth
Debug Message: Disabling persisent auth. User will need to login manually.
Debug Message: No existing persistent auth credentials were found for automatic login.
Debug Message: Initialize Prefs
Debug Message: Checking data binaries
DebugMessage: Force Clean generated files: 0
DebugMessage: Force Clean generated files: 0
DebugMessage: Force Clean generated files: 0
DebugMessage: Force Clean generated files: 0
Debug Message: Social overlay is disabled due to overlay setup failure (EOS_UnexpectedError).
Debug Message: [EOS SDK] Connect Login Complete - ProductUserId: 0002a603bf4440428c21ea5e3113c5fa
DebugMessage: Force Clean generated files: 0
DebugMessage: Force Clean generated files: 0
DebugMessage: Force Clean generated files: 0
DebugMessage: Force Clean generated files: 0
DebugMessage: Force Clean generated files: 0
Debug Message: Loading core binary
DebugMessage: Force Clean generated files: 0
DebugMessage: Force Clean generated files: 0
Debug Message: Core XML has been changed: Yes
Debug Message: Setting core data
Debug Message: Loading particles binary
Debug Message: Setting particle data
Debug Message: Registering types
Debug Message: Setting data for assets
Debug Message: Activation successful.
Debug Message: Checking virtual memory
Debug Message: Initializing event center
Debug Message: Checking for valid working directory
Debug Message: Entering WinMain
Debug Message: ******* Starting Game Shell *******
Debug Message: InitializeResources.
DebugMessage: Force Clean generated files: 0
DebugMessage: Force Clean generated files: 0
DebugMessage: Force Clean generated files: 0
DebugMessage: Force Clean generated files: 0
DebugMessage: Force Clean generated files: 0
DebugMessage: Force Clean generated files: 0
Debug Message: Initializing Shell
Debug Message: Initializing Fonts
Debug Message: RegisterFont: Font with file: BankGthd.ttf, face index: 0, size 18 ALREADY registered, ID of -245753110 with same properties will not be registered separately.
Debug Message: Initializing Fonts - complete
Debug Message: Initializing Direct3D
DebugMessage: Particle Engine Created.
Debug Message: Adding DXSAS clean up function
Debug Message: Initializing device
Debug Message: DrawManager InitializeDevice
Debug Message: Creating renderer
Debug Message: Initializing Direct3D 11 Renderer
DebugMessage: Force Clean generated files: 0
Debug Message: Creating FBX animation core
Debug Message: Enumerating device settings
Debug Message: CD3D11RendererSettings::Enumerate: Preferred adapter is 0
Debug Message: CD3D11RendererSettings::Enumerate: Creating DXGI 1.1 factory
Now im not familiar with the debug lines of GC3 but the only obvious error to me is that login fail for this EOS SDK but i believe that is just an Epic Games launcher thing so shouldn't be an issue with it being installed through steam.