On Catalina you should have Photos 5.0 installed and not Photos 3.
Perhaps you have been using a link on the Desktop or a Dock icon that is still linked to an over version of Photos on a backup drive or somewhere.
Try to launch Photos by double clicking the Photos icon in the Applications folder, not some link on the Desktop or in the Dock. This should launch the current version of Photos.
To open an older Photos Library in Photos 5.0 hold down the options key ⌥ while launching Photos 5.0.
Release the key, when the library chooser dialog appears, then select the older library you want to open.