Yes, Values can't be passed between the process. There is an indirect way of doing it.
In the second process, Call IICS Rest API(Mapping) for the first task flow or any specific mapping for which values are stored as IN-OUT parameters
Retrieve the list of parameters from the REST call and find the matching parameters & Retrieve the current value of that. Assign this value to the current process to execute. It will be a tedious way of achieving it.