In $\triangle$-SCF, the wavefunctions of different states are not orthogonal to each other. You would require NOCI (non-orthogonal CI) type formalism to obtain the transition dipole moment.

You might wanna take a look at #1697

You can use the code like https://github.com/pyscf/pyscf-forge/blob/bb743d16ecf997d935e32a3740f41991ad57882a/pyscf/msdft/noci.py#L152
to compute the density matrix between the two determinants, then the scf.hf.dip_moment(mol, dm) for the transition dipole.