Is it possible to show custom tasks from a wid file in the palette of tasks in the VSCode BPMN2 editor? If not, is there another way to add custom tasks to a business process?
yes, it is possible, but there are some limitations. See this article.
Please, pay attention that only one VS Code project can be opened at a time and other restrictions mentioned in the article.
Also, you may be interested to check alternatives to WID task, see pros and cons for different custom logic types in this article.