=== manual installation  using system QT (abandoned) ===
Instead of using the dev_setup.sh use the following commands to do the setup
* sudo apt-get install -y git-core g++ cmake extra-cmake-modules kio-dev gettext pkg-config
* sudo apt-get install -y pkg-kde-tools qtbase5-dev qtdeclarative5-dev kio-dev
* sudo apt-get install -y libqt5websockets5-dev libkf5i18n-dev libkf5notifications-dev libkf5plasma-dev libkf5kio-dev
then install the additional packages for libqt5webview5-dev manually
=== additional debian packages ===
download the deb files:
* wget http://ftp.de.debian.org/debian/pool/main/q/qtwebview-opensource-src/libqt5webview5-dev_5.11.3-2_armhf.deb
* wget http://ftp.de.debian.org/debian/pool/main/q/qtwebview-opensource-src/libqt5webview5_5.11.3-2_armhf.deb
* wget http://ftp.de.debian.org/debian/pool/main/q/qtwebengine-opensource-src/libqt5webengine5_5.11.3+dfsg-2+deb10u1_armhf.deb
* wget http://ftp.de.debian.org/debian/pool/main/q/qtwebengine-opensource-src/libqt5webenginecore5_5.11.3+dfsg-2+deb10u1_armhf.deb

install with:
* sudo apt install ./libqt5webenginecore5_5.11.3+dfsg-2+deb10u1_armhf.deb 
* sudo apt install ./libqt5webengine5_5.11.3+dfsg-2+deb10u1_armhf.deb 
* sudo apt install ./libqt5webview5_5.11.3-2_armhf.deb 
* sudo apt install ./libqt5webview5-dev_5.11.3-2_armhf.deb
=== continue setup ===
* mkdir -p build-testing
* cd build-testing
clean if the directory already existed
* rm -r *
* cmake .. -DCMAKE_INSTALL_PREFIX=/usr -DCMAKE_BUILD_TYPE=Release   -DKDE_INSTALL_LIBDIR=lib -DKDE_INSTALL_USE_QT_SYS_PATHS=ON
* make -j4
* sudo make install
* cd ..
build lottie
* rm -rf lottie-qml/
* git clone https://github.com/kbroulik/lottie-qml
* cd lottie-qml
* mkdir build
* cd build
* cmake .. -DCMAKE_INSTALL_PREFIX=/usr -DCMAKE_BUILD_TYPE=Release   -DKDE_INSTALL_LIBDIR=lib -DKDE_INSTALL_USE_QT_SYS_PATHS=ON
* make
* sudo make install

...

I gave up on this approach because the system QT is designed and built to be used with a complete X11 stack and that was not my idea.
In addition the QML of the GUI is using the KDE framwork Kirigami and needs version 2.7 which is a lot newer than what the system packages provide.