These are the packages that would be merged, in order:

Calculating dependencies ... done!
Dependency resolution took 1.06 s (backtrack: 0/20).

[ebuild  N     ] app-misc/tmux-3.8::gentoo  USE="-debug -jemalloc (-selinux) -sixel (-systemd) -utempter -vim-syntax" 875 KiB
[ebuild  N     ] app-misc/tmux-xpanes-4.2.0::gentoo  66 KiB

Total: 2 packages (2 new), Size of downloads: 941 KiB