Found from https://www.makeuseof.com/create-your-own-fonts-with-glyphtracer-linux/
That tutorial is good but incomplete. The complete way goes like
sudo apt install python-pip-whl
sudo apt install python3-pip potrace git fontforge
pip3 install pyqt5
mkdir omatfontit
cd omatfontit
git clone https://github.com/jpakkane/glyphtracer.git
cd glyphtracer
sudo python3 setup.py install
glyphtracer.py
convert -monochrome abc.png uusi-abc.png
