Changing default key send inside terminal to <C-Q> instead of <C-W> in terminal mode in vim

Question

I want to send keys to a terminal open inside vim using <C-Q> instead of <C-W>. When I run the command :set termwinkey=<C-Q> inside vim I get the error message E518: Unknown option: termwinkey=<C-q>. I can open terminals inside vim. So why does vim not recognise this option ?

[EDIT] output of :version as asked

VIM - Vi IMproved 8.0 (2016 Sep 12, compiled Oct 13 2020 15:49:09)
Included patches: 1-1453
Modified by pkg-vim-maintainers@lists.alioth.debian.org
Compiled by pkg-vim-maintainers@lists.alioth.debian.org
Huge version with GTK2 GUI.  Features included (+) or not (-):
+acl               +clientserver      +dialog_con_gui    +find_in_path      +keymap            +modify_fname      +multi_byte        +profile           +statusline        +textobjects       +wildignore
+arabic            +clipboard         +diff              +float             +lambda            +mouse             +multi_lang        -python            -sun_workshop      +timers            +wildmenu
+autocmd           +cmdline_compl     +digraphs          +folding           +langmap           +mouseshape        -mzscheme          +python3           +syntax            +title             +windows
-autoservername    +cmdline_hist      +dnd               -footer            +libcall           +mouse_dec         +netbeans_intg     +quickfix          +tag_binary        +toolbar           +writebackup
+balloon_eval      +cmdline_info      -ebcdic            +fork()            +linebreak         +mouse_gpm         +num64             +reltime           +tag_old_static    +user_commands     +X11
+balloon_eval_term +comments          +emacs_tags        +gettext           +lispindent        -mouse_jsbterm     +packages          +rightleft         -tag_any_white     +vertsplit         -xfontset
+browse            +conceal           +eval              -hangul_input      +listcmds          +mouse_netterm     +path_extra        +ruby              +tcl               +virtualedit       +xim
++builtin_terms    +cryptv            +ex_extra          +iconv             +localmap          +mouse_sgr         +perl              +scrollbind        +termguicolors     +visual            +xpm
+byte_offset       +cscope            +extra_search      +insert_expand     +lua               -mouse_sysmouse    +persistent_undo   +signs             +terminal          +visualextra       +xsmp_interact
+channel           +cursorbind        +farsi             +job               +menu              +mouse_urxvt       +postscript        +smartindent       +terminfo          +viminfo           +xterm_clipboard
+cindent           +cursorshape       +file_in_path      +jumplist          +mksession         +mouse_xterm       +printer           +startuptime       +termresponse      +vreplace          -xterm_save
   system vimrc file: "$VIM/vimrc"
     user vimrc file: "$HOME/.vimrc"
 2nd user vimrc file: "~/.vim/vimrc"
      user exrc file: "$HOME/.exrc"
  system gvimrc file: "$VIM/gvimrc"
    user gvimrc file: "$HOME/.gvimrc"
2nd user gvimrc file: "~/.vim/gvimrc"
       defaults file: "$VIMRUNTIME/defaults.vim"
    system menu file: "$VIMRUNTIME/menu.vim"
  fall-back for $VIM: "/usr/share/vim"
Compilation: gcc -c -I. -Iproto -DHAVE_CONFIG_H -DFEAT_GUI_GTK  -pthread -I/usr/include/gtk-2.0 -I/usr/lib/x86_64-linux-gnu/gtk-2.0/include -I/usr/include/gio-unix-2.0/ -I/usr/include/cairo -I/usr/include/pango-1.0 -I/usr/include/atk-1.0 -I/usr/include/cairo -I/usr/include/pixman-1 -I/usr/include/gdk-pixbuf-2.0 -I/usr/include/libpng16 -I/usr/include/pango-1.0 -I/usr/include/harfbuzz -I/usr/include/pango-1.0 -I/usr/include/glib-2.0 -I/usr/lib/x86_64-linux-gnu/glib-2.0/include -I/usr/include/freetype2 -I/usr/include/libpng16 -I/usr/include/freetype2 -I/usr/include/libpng16 -Wdate-time  -g -O2 -fdebug-prefix-map=/build/vim-EfP9JP/vim-8.0.1453=. -fstack-protector-strong -Wformat -Werror=format-security -U_FORTIFY_SOURCE -D_FORTIFY_SOURCE=1       
Linking: gcc   -L. -Wl,-Bsymbolic-functions -Wl,-z,relro -Wl,-z,now -fstack-protector -rdynamic -Wl,-export-dynamic -Wl,-E  -Wl,-Bsymbolic-functions -Wl,-z,relro -Wl,-z,now -Wl,--as-needed -o vim   -lgtk-x11-2.0 -lgdk-x11-2.0 -lpangocairo-1.0 -latk-1.0 -lcairo -lgdk_pixbuf-2.0 -lgio-2.0 -lpangoft2-1.0 -lpango-1.0 -lgobject-2.0 -lglib-2.0 -lfontconfig -lfreetype -lSM -lICE -lXpm -lXt -lX11 -lXdmcp -lSM -lICE  -lm -ltinfo -lnsl  -lselinux  -lacl -lattr -lgpm -ldl  -L/usr/lib -llua5.2 -Wl,-E  -fstack-protector-strong -L/usr/local/lib  -L/usr/lib/x86_64-linux-gnu/perl/5.26/CORE -lperl -ldl -lm -lpthread -lcrypt  -L/usr/lib/python3.6/config-3.6m-x86_64-linux-gnu -lpython3.6m -lpthread -ldl -lutil -lm -L/usr/lib/x86_64-linux-gnu -ltcl8.6 -ldl -lz -lpthread -lm -lruby-2.5 -lpthread -lgmp -ldl -lcrypt -lm     

Answer 1

You must update Vim to v8.1 or later.