I guess we should use the current ip neighbor xxx instead of old arp. I hope it does the same.
sudo ip neighbor add proxy 192.0.2.1 dev eth0 sudo ip -6 neigh add proxy aa::1 dev eth0
Show
vyos@r1# sudo ip neighbor show proxy 192.168.122.11 dev eth0 proxy 192.0.2.1 dev eth0 proxy aa::1 dev eth0 proxy [edit] vyos@r1#