Adding device handlers was an advanced feature of the original SmartThings architecture. However, ST is in the middle of a transition to an entirely new architecture, and Device Type Handlers will no longer be used. One of the stated goals is to make it easier for both device manufacturers and end users to support advanced device features. See the following:
FAQ: I have no idea what Edge is. Is that a new developer tool? (2022)
Anyway, you don’t need the developer workspace (which is part of the new architecture) just to add a custom Groovy device type handler. For that you need the IDE from the old architecture.
If you are in North America.