Void Linux does not ship with the tmux-256color terminal definition (terminfo) by default. Without this definition, running tmux with set -g default-terminal "tmux-256color" will cause terminal applications (and line editors like zsh) to fall back to a dumb terminal mode, resulting in characters incorrectly echoing and overlapping on the prompt.
To fix this and enable proper truecolor and italics support inside tmux, download and compile the terminal definitions locally:
# Download the latest terminfo source file
curl -LO https://invisible-island.net/datafiles/current/terminfo.src.gz
# Extract the source file
gunzip terminfo.src.gz
# Compile the tmux-256color terminfo definition into your ~/.terminfo directory
tic -x -e tmux-256color terminfo.src
# Clean up
rm terminfo.srcAfter installing the terminfo file, fully restart the tmux server:
tmux kill-server
tmux