Per :h FileType the FileType event doesn't do anything unless 'filetype' is set. The standard way to set that is to have this in your vimrc/init.vim:
This "enables file type detection".
You don't have anything in your init.vim so that's surely why this stuff isn't working "out of the box". Your Session.vim file, which contains a bunch of ...
I am using Neovim both on Linux, Mac and Windows. For terminal Neovim, it seems that ctrl + 6 works as expected for me. On Windows, Ctrl-6 does not work. FYI, the terminal I am using for different platform:
Linux: mintty (Connected to remote Linux server via ssh)
Mac: Either iterm2, Alacritty, Kitty works.
For Neovim GUI client, you can ...
justinmk (current neovim leader?) states
ctrl-6 only works by accident in some terminals. The actual builtin mapping is <C-^>.
There is also https://github.com/equalsraf/neovim-qt/issues/170
So it just doesn't work for neovim (nvim.exe and nvim-qt.exe) even though neovim help is ...
Popup menu in neovim-qt is controlled by GuiPopupmenu command.
You should add it to you ginit.vim:
It is not documented that well, I've found it somewhere in github issues.
You can also try look into neovim-qt shim layer to find out what else is there: