Warning (files): Missing `lexical-binding' cookie in "/nix/store/vwsqyqcsf7brb9crnz94jrzgkh4qcygl-mk-wrapper-subdirs.el".
You can add one with `M-x elisp-enable-lexical-binding RET'.
See `(elisp)Selecting Lisp Dialect' and `(elisp)Converting to Lexical Binding'
for more information.