You can try these commands to solve the node v10 required:
export NVM_DIR="$HOME/.nvm"
[ -s "$NVM_DIR/nvm.sh" ] && \. "$NVM_DIR/nvm.sh"
nvm install 10.22.1
They are effective only in the current shell, so you have either to place them in ~/.bashrc or ~/.profile, or to run them manually before starting Duniter. (if node v10.22.1 is already installed, it will not reinstall it, but without this command I cannot run or build Duniter)
Unless you want to contribute to the Duniter development or to use GVA (the new HTTP API yet unstable and unreleased), it will be simpler to install the .deb.