I finally got round to trying to install debian-sparc in an LDOM on my T4 server.
Sadly, this didn't work.
With Debian 12, software installation fails. I see
Jun 10 08:43:02 in-target: The following packages have unmet dependencies:
Jun 10 08:43:03 in-target: console-setup-linux : Depends: keyboard-configuration (= 1.220) but 1.227 is installed
along with some unrelated dpkg-deb segfaults. Ignoring that, the bootloader