Upstream is replacing sxiv by nsxiv.

This command sequence should allow for a seamless transition for any Beast user:

XDG_CONFIG_HOME="${XDG_CONFIG_HOME:-$HOME/.config}"
mv "$XDG_CONFIG_HOME/sxiv" "$XDG_CONFIG_HOME/nsxiv"
ln -s "$XDG_CONFIG_HOME/nsxiv" "$XDG_CONFIG_HOME/sxiv"

Specifically, the above mitigates this error:

sxiv: /home/<user>/.config/nsxiv/exec/key-handler: No such file or directory