@tintinux
I can't use the OPM because for any package selected the buttons are always disabled.
Unfortunately I don't have Ubuntu 20.04, so I cannot test. In order to enable the download/install/update buttons, you have to check the checkbox in front of the package(not select). This behaviour did not change since 4-5 years, I cannot recall exactly. If still not works, please let me know.
PS: Maybe somebody with Unbuntu 20.04 can run a few test?