/usr/share/texmacs/TeXmacs/plugins/maxima/ is in texmacs-common 1:1.0.7.18-1.
This file is owned by root:root, with mode 0o755.
..
/usr/share/texmacs/TeXmacs/plugins/maxima/doc/
/usr/share/texmacs/TeXmacs/plugins/maxima/doc/maxima-abstract.en.tm
/usr/share/texmacs/TeXmacs/plugins/maxima/doc/maxima-demo.en.tm
/usr/share/texmacs/TeXmacs/plugins/maxima/doc/maxima-demo.it.tm
/usr/share/texmacs/TeXmacs/plugins/maxima/doc/maxima.en.tm
/usr/share/texmacs/TeXmacs/plugins/maxima/lisp/
/usr/share/texmacs/TeXmacs/plugins/maxima/lisp/texmacs-maxima.lisp
/usr/share/texmacs/TeXmacs/plugins/maxima/packages/
/usr/share/texmacs/TeXmacs/plugins/maxima/packages/session/
/usr/share/texmacs/TeXmacs/plugins/maxima/packages/session/maxima.ts
/usr/share/texmacs/TeXmacs/plugins/maxima/progs/
/usr/share/texmacs/TeXmacs/plugins/maxima/progs/init-maxima.scm
/usr/share/texmacs/TeXmacs/plugins/maxima/progs/maxima-input.scm
/usr/share/texmacs/TeXmacs/plugins/maxima/progs/maxima-kbd.scm
/usr/share/texmacs/TeXmacs/plugins/maxima/progs/maxima-menus.scm