Solution found:
I followed the advice in this article here: VS Code C++ Intellisense in UE 5.3 not recognizing certain parts of code - #12 by goosinator - Ask - GameDev.tv
Basically, I shut down VSCode, deleted the following folders, and reinstalled.
C:\Users\me\AppData\Roaming\Code
C:\Users\me.vscode
I did have to re-create my VSCode project from UE since something config wise was lost.
Luckily I had everything backed up on a git branch, so I could re-create then copy my code over.
Also, my previous post said that it looked like CoreMinimal.h was a problem, but ModuleManager.h was not, but when I reversed the order of the includes, then ModuleManager showed up as a problem and CoreMinimal did not, so I think intellisense was just stopping at the first error.
Another factor was that I had both clangd and the C++ extension fighting over intellisense, I disabled clangd for this workspace.