Setup/Debug problem with VSTA

Hi folks,

I want to write tools for Designer using C#. The result should be a DLL. Unfortunately, I can't figure out how to get there (I do have extensive experience working on large C projects in VS).
So here is what I have so far:
- installed VS Community
- installed VS for applications
- installed Corel Suite 2020
- installed Corel templates for VS
- in the Scripts Docker, I clicked on "Visual Studio Tools for Applications->New macro project".

I'm able to launch VSTA via the Tools->Script menu in Designer.
I tried to follow these instructions as much as possible (seems to describe a slightly different setup):

It is possible to build the project (just a simple line tool), but that's about it. If I continue to follow the instructions to run the Debugger, I see an error message: "Cannot start debugging. Pre-debugging negotiations with Host failed."
What am I doing wrong?

Also, I found the project and source code in this temp folder:

Why would anybody place sources in a temp folder? How can I change this?

Thanks for your help, it's very much appreciated.

PS: I have to use CD 2020 for certain reasons, and can't go back to older versions.
The problem has appeared here as well: