https://apt.syncthing.net/

# Note: this command line was not needed on the Ubuntu 23.10 version:
sudo mkdir -p /etc/apt/keyrings

sudo curl -L -o /etc/apt/keyrings/syncthing-archive-keyring.gpg https://syncthing.net/release-key.gpg

# Stable Channel
echo "deb [signed-by=/etc/apt/keyrings/syncthing-archive-keyring.gpg] https://apt.syncthing.net/ syncthing stable" | sudo tee /etc/apt/sources.list.d/syncthing.list

sudo apt-get update
sudo apt-get install syncthing

# Set syncthing to start on boot
https://docs.syncthing.net/users/autostart.html#linux

# Note: replace myuser below with the userID you login to Ubuntu
sudo systemctl status syncthing@myuser.service
sudo systemctl enable syncthing@myuser.service
sudo systemctl start syncthing@myuser.service
sudo systemctl status syncthing@myuser.service
Note: Get local web link to configure syncthing from above status command output
Example: 127.0.0.1:8384

Open web link in Ubuntu browser to configure syncthing:
Example:
http://127.0.0.1:8384