I installed Amarok from ppa of Pedro (Pedro de Carvalho Gomes: https://launchpad.net/~pgomes/+archive/ubuntu/amarok?field.series_filter=focal).
The central panel, the context panel, appears just blank, nothing to add or set.

Kubuntu 20.04
KDE Plasma Version 5.18.5
KDE Frameworks Version 5.68.0
Qt Version 5.12.8
Kernel Version 5.4.0-66

I just used the installer (aptitude install amarok) and no error was reported.
Any insight?
should I installed from source (from the .tar.xz file)? using cmake and all the instructions here:https://community.kde.org/Amarok/Development/Compiling
Guess that I have to change the instructions, where it says kde4 put kde5

There is no such thing as KDE5, this should be replaced by Plasma or kf5. Sadly the complete installation instructions need an overhaul, not sure this is still relevant, I haven't used it in years. Since Pedro updates his PPA on a very regular basis this shouldn't be needed anyway,.

Strange you have a blank central panel though, I use Pedros PPA as well, although on a more recent Kubuntu installation than you, and my panel shows.

Find the problem!!! and solved!
I run amarok from terminal with -d option. I found message of missing icons (same messages as I run xdg-open from a terminal)
I was using another ser o icons! I set in the "Settings" the "Humanity" set of icons. I changed to the "Oxygen" set. I erase all the amarok settings (in .config, .kde, .local so on and so forth) .
I have now a fully operational amarok. Great job! Thank you all of the team.