Install Syncthing

https://apt.syncthing.net/

apt install -y curl apt-transport-https ca-certificates
curl -L -o /etc/apt/keyrings/syncthing-archive-keyring.gpg https://syncthing.net/release-key.gpg
echo "deb [signed-by=/etc/apt/keyrings/syncthing-archive-keyring.gpg] https://apt.syncthing.net/ syncthing stable-v2" | tee /etc/apt/sources.list.d/syncthing.list
apt update
apt install -y syncthing

Create User Syncthing with Home Folder on HDD-Housing Storage

useradd -m -s /bin/bash -d /poolname/syncthing -u 1110 -g 1110 syncthing
echo "syncthing:$(openssl rand -base64 100 | tr -d '=+/\n\r' | cut -c 1-70)" | chpasswd
systemctl enable --now syncthing@syncthing
systemctl status syncthing@syncthing  # shows used ip and port

Replace "poolname" with your actual poolname.