When LR6 tries to open an LR5 catalog, it correctly prompts to convert the old catalog to the new format. Unfortunately, the user does not get to pick the destination name nor path. It would be nice if we were given that choice.
As an EXPERIENCED user the ability to upgrade the catalog to a different folder location allowed the safety if the upgrade process failed. It also allows quick checking of what Catalogs have been upgraded LR3_, LR4_ .. LR6_. The new process may work great if you have a limited number of Catalogs; but when working with numerous historical short lived Catalogs the new limiting ability falls decidedly short. Please return the old functionality . The current help documentation still reflects the old ability