Comment 1 for bug 1879353

This is happening to me too. I'm not too sure what the installer script doesn't like about the version of 'gtk2-engines-pixbuf' here:
sudo apt list -i gtk2-engines-pixbuf
Listing... Done
gtk2-engines-pixbuf/focal,now 2.24.32-4ubuntu4 amd64 [installed]

Regarding the other errors about the missing 'python-*' dependencies, well, these are missing indeed on Focal Fossa. Quick check via https://packages.ubuntu.com shows such packages were last used on Eoan Ermine (Ubuntu 19.10). What we have on 20.04 are 'python3-pyqt5', 'python3-dbus.mainloop.pyqt5', 'python3-reportlab' and 'python3-notify2'.