Make it a web app and your cheap entry level grads can do it.
It was no biggie, just joining the low level of C with the class notions from Java. Pair that with the C++FAQ website, and it was easy.
Are entry-level devs generally not able to do that nowadays? I do not believe people are generally more stupid or less capable, so, is education so much worse or what's going on?
If a PM needs NotepadAI for their career progression then start it from scratch.
These days it would have to be written in some other language that has those Windows Runtime bindings available for it. So could be C++ but if I were to guess I'd say it's written in Typescript and compiled to a native or .Net binary.
As far as I remember, Notepad was the reference implementation for a Microsoft widget. Nothing more. If "modern entry-mid level devs can't do that" you really have a much bigger problem.