I have the minimal document here:
\documentclass{article}
\usepackage{unicode-math}
\usepackage{listings}
\setmainfont{Stix}
\setmathfont{Latin Modern Math}
\setmonofont{Fira Mono}
\begin{document}
this is λ lambda
$$\int_0^\infty λ\lambda$$
\begin{lstlisting}
# some random pseudocode using unicode
def function(λ):
αδ = βθ
def function( λ):
pass
\end{lstlisting}
\end{document}
producing with lualatex:
Look at how the unicode characters are rendered in the listing, but not in the right place.