I am also having this issue after upgrading to Unity 2023.2.8 and grabbing the latest version of iOS Project Builder for Unity (3.61.1). I was on XCode 14 and iOS 16 or something I think, but I've updated everything to the latest stable version and still have the issue.

Windows Version: 11
Builder Version: 3.61.1
iOS SDK Version: 17.2 (XCode 15.2)
Unity Version: 2023.2.8

In file included from .\MainApp\main.mm:1:
.\UnityFramework/UnityFramework.h(4,9): fatal error: 'UnityFramework/UnityAppController.h' file not found
#import <UnityFramework/UnityAppController.h>