in.tftpd doesn't exist anymore. Instead of xinetd, use tftpd-hpa and put the files on the /srv/tftp directory.Install xinetd and tftpd.
sudo apt install xinetd tftpd
/etc/xinetd.d/tftp
service tftp
{
socket_type = dgram
protocol = udp
wait = yes
user = root
server = /usr/sbin/in.tftpd
server_args = -s /tftpboot
disable = no
}
Restart xinetd to apply changes.
sudo systemctl restart xinetd