Hi Guido,
You are correct that, unfortunately, the Workbench has not been updated to support the modern PacletObject[<| ... |>] syntax for paclets. Our development efforts have instead been focused on improving the capabilities available in Wolfram Language itself for creating and developing paclets.
For example, the DocumentationTools and PacletTools packages have undergone significant development over the last few WL versions, adding support for creating paclets and authoring and building documentation that previously was exclusively available in the Workbench. While the Workbench does have a few remaining capabilities that don't have a direct analog in WL, our work has focused on bringing WL up to par with and surpassing the Workbench.
For example, as part of the recently released Wolfram Paclet Repository (https://paclets.com), we created a new Paclet Resource Definition Notebook tool that includes a GUI toolbar (see screenshot) for building documentation and privately or publicly sharing a paclet in the Wolfram Cloud, that additionally performs nice quality-of-life checks like linting for possible mistakes in your WL source code.
If you're interested in these tools, you might also be interested in this ad hoc collection of links I've put together that points to some of the useful documentation and presentations we've done describing our work in this area:
https://www.wolframcloud.com/obj/connorg/Published/Paclet_Development_Resources.nb
I apologize for the issues you've had using the Workbench, but I hope that these new tools serve as a powerful and easy to use alternative. Work to improve and expand them is ongoing, so I would welcome any feedback you may have — please don't hesitate to reach out.
Connor
