Reinstalling now has the Windows directory in "C:\Program Files\Epic Games\UE_5.5\Engine\Config" but there is still no Windows development option in the Epic Launcher’s Unreal Engine options. Perhaps it is simply a default, and/or I have experienced a number of simultaneous issues.
Suffice that reinstallation of UE did NOT solve the “Platform Win64 is not a valid platform to build. Check that the SDK is installed properly and that you have the necessary platform support files (DataDrivenPlatformInfo.ini, SDK.json, etc).” error.