Jumping in here to share some of my own info as I'm having the same issue.

brad@kazuki:~/ > nvim
zsh: segmentation fault  nvim

I've got neovim installed in the system profile (so root has a comfortable
editor instead of just nano)
guix (GNU Guix) d22d246a256814784dfb03437949bdc2efd746a5
brad@kazuki:~/ > echo $TERM
screen-256color
Here is my $TERM. I am running inside tmux using termite as my terminal
emulator.
For the record I get the same segmentation fault outside of tmux using the
same terminal emulator.
brad@kazuki:~/ > echo $TERM
xterm-termite

I tried the guix environment --container command that Ricardo shared and in
that instance nvim works for me in tmux just fine as well. If there's more
info about my environment I can share to help track down the issue, please
let me know.