Maybe I'm going about all of this the wrong way? I just want a Windows machine that would handle most of the popular games out there that would support the use of Unity.
Unity would probably work under windows 11, since Windows is generally good at backwards compatibility. However, I can't confirm myself since I don't use windows or Unity. Perhaps ask if your son would consider using Godot instead of Unity in case it doesn't work (or even if it does, since Godot is the better engine for most use cases anyway IMO).
Godot is great for game development AFAIK. However, my son wants to use the software for more than just gaming. It's something that we'd consider and thank you for responding.
EDIT: My son just told me that he would use said software primarily for gaming. So, you may have just given us the solution with the Godot recommendation. Thanks again!