Hi, see this question:
tex.stackexchange.com/q/574974/4736 . It is about having multicols with different widths. This is a quite frequent question. The answers and packages (at least their concepts) all are from pre-LuaTeX age. As far as I understood LuaTeX, we can tamper with some internals of TeX. Or are the new hooks of LaTeX3 a good starting point for enhancing the multicol package? -- Before you ask, sorry, I'm only a user...