Confirmed fixed with chromium-browser 81.0.4044.129-0ubuntu0.20.04.1 from focal-proposed.
I verified update-alternatives couldn't be used to set the default value of [x-www-browser|gnome-www-browser] to /usr/bin/chromium-browser in a fully up-to-date focal VM, then I enabled focal-proposed for universe, ran "apt update" and "apt dist-upgrade" to install the updated chromium-browser package, and I verified that update-alternatives now accepted to set the default x-www-browser|gnome-www-browser. I also verified that running x-www-browser|gnome-www-browser did launch chromium-browser, as expected.
Confirmed fixed with chromium-browser 81.0.4044. 129-0ubuntu0. 20.04.1 from focal-proposed.
I verified update-alternatives couldn't be used to set the default value of [x-www- browser| gnome-www- browser] to /usr/bin/ chromium- browser in a fully up-to-date focal VM, then I enabled focal-proposed for universe, ran "apt update" and "apt dist-upgrade" to install the updated chromium-browser package, and I verified that update-alternatives now accepted to set the default x-www-browser| gnome-www- browser. I also verified that running x-www-browser| gnome-www- browser did launch chromium-browser, as expected.