WireGuard and lsyncd to sync a directory.

install wireguard

apt install wireguard / pacman install wireguard-tools

generate keypairs

wg genkey | tee server_private.key | wg pubkey > server_public.key

Server config file /etc/wireguard/wg0.conf

[Interface]
PrivateKey = <server_private_key>
Address = 10.11.12.1/24
ListenPort = 51820

[Peer]
PublicKey = <client1_public_key>
AllowedIPs = 10.11.12.2/32

[Peer]
PublicKey = <client2_public_key>
AllowedIPs = 10.11.12.3/32

# Repeat for all clients...