Comment 6 for bug 2040080

Reproduction is easy:

$ lxc launch images:ubuntu/23.10/desktop ubuntu --vm -c limits.cpu=4 -c limits.memory=4GiB --console=vga

In the VM:

$ sudo apt update -y
$ sudo apt install -y tmux alacritty
$ echo "set -g mouse on" > ~/.tmux.conf:
$ alacritty
$ tmux
# Write text, highlight with mouse, try to paste and see no text is copied

Testing the fix with current debian unstable package
$ wget http://ftp.us.debian.org/debian/pool/main/t/tmux/tmux_3.3a-5_amd64.deb
$ sudo dpkg -i tmux_3.3a-5_amd64.deb
$ tmux
# write some text, highlight with mouse, and see text will be pasted