Jumping in here to share some of my own info as I'm having the same issue.
address@hidden:~/ > 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
address@hidden:~/ > 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.
address@hidden:~/ > 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.