You can download the pre-built binaries into a new node instance subfolder with this command sequence on your ARM-based RockPi device.
Please set the RELEASE value first to the version you want to use. You can find the latest release at https://github.com/input-output-hk/jormungandr/releases/latest
mkdir ~/jormungandr-node cd ~/jormungandr-node RELEASE="0.5.0" ARCHITECTURE="aarch64" FILE="jormungandr-v"$RELEASE"-"$ARCHITECTURE"-unknown-linux-gnu.tar.gz" wget "https://github.com/input-output-hk/jormungandr/releases/download/v"$RELEASE"/$FILE" tar -xzf $FILE rm $FILE
You now can execute both jormungandr and jcli with a leading ./ prefix
./jormungandr --version ./jcli --full-version