I may have touched on some of these in my workarounds thread but there are some programs which I currently cannot use because packages are not available/installable in Debian 10's ppc64le (whereas the same packages are available on amd64):
openshot-qt (python3-openshot but it is not installable)
mozc (I did not investigate the cause, but anthy is works instead)
anki (python3-pyqt5.qtwebengine (> 5.11) but it is not installable)
mupen64plus-qt (plugin packages are available but the main binary package is not)
dolphin-emu (data package is available, main package is not)
obs-studio
0ad
openmorrowind
And not ppc specific but; is Xonotic left out of Debian because Nexuiz is maintained in its place?