Update for my situation: I had the ‘Script Plugin’ enabled in my project, and that appeared to be the root cause of ‘ScriptGeneratorUbtPlugin.dll not found’ issue. Perhaps ‘Script Plugin’ doesn’t even apply to projects based on a binary distribution…
So after a removing the reference to that plugin, and a few C++ project code modifications due to UE_50 → UE51 changes, the project is building again, in Visual Studio 2022 w/ v142 toolchain.