mylatex: \makeatletter is considered an undefined control sequence

[matteocoder]

I was trying to use mylatex, but compilation stops right at the beginning returning an "Undefined control sequence l.126 \makeatletter" error.
Here is the mwe:

\documentclass{article}
\usepackage{fontspec}
\usepackage{lipsum,showframe}
\begin{document}
\lipsum
\end{document}

which I tried to compile using lualatex -ini mylatex.ltx mwe.
I tried compiling this on Windows 10 Home 64-bit 1909 with TeXLive 2020 updated on the 28th of October.

[davidcarlisle]

You need to load the lualatex format

lualatex -ini "&lualatex" mylatex.ltx mwe

[matteocoder]

@davidcarlisle Thank you for your reply.