OpenMPI 5 drops 32-bit support, but otherwise does not change the API/ABI.
So it is technically not a transition, but breaks 32-bit builds.
Doesn't make it better. This is not the time to do that without tests
builds and bugs filed.
The solution is changing mpi-defaults to MPICH for 32-bit archs. MPICH
builds on all archs, but testing all dependencies of the change has not been
tested, and I don't know how you would do that - setting up eg ratt to
rebuild all on 32-bit archs (as everything on 64-bit will not have changed.)
Beside the easy part of chaning mpi-defaults, I count 30 something
packages that have explicit build dependencies on libopenmpi-dev. None
of those packages has bugs filed to change to mpich on 32 bit
architectures.
To be honest, I don't see these two changes (changing mpi-defaults to
mpich on 32 bit; breaking 32 bit build of openmpi) to be ready. It'd be
preferable to reinstate a 32-bit compatible pmix and fix openmpi on 32
bit until the time_t transition is done.
Cheers