Hi Kimiaki,the "cairosvg" package is only available in buster-backports on your installation. So when running "apt install cairosvg" you are automatically selecting cairosvg-2.4.2-1~bpo10+1 from the buster-backports archive.
python3-cairosvg is not found because you told apt to only use the main archive. Instead please run:
apt -t buster-backports install cairosvg Regards, Michael
