Rigid body dynamics system and solver is a completely different solver to transient Structural solver (see help manual for more info).
Rigid dynamics is aimed for rigid body dynamics (say how a mechanism moves), while transient can be used for impact (flexible bodies), earthquake analysis in time domain, shock loads, etc, but not so much for rigid body dynamics (there we use the other system or in 2023 R1 Ansys motion which is also aimed for rigid body dynamics).
As for the original question, what you do when you connect them to each other as you show, is to transfer over data (loads or displacements on cut boundaries) in order to do a submodel analysis. See what that means (sub-modelling) and how it is done (static or transient system is the same with regards to submodel).
All the best