When "which columns to show" setting is set to "in the query" (the default) and the Fetch XML query has no attribute tags (returning all columns), an ArgumentNullException is thrown when clicking the Add button. To workaround I had to add an attribute (or use a view), then click Add in order to get to the settings and select "everything" for "which columns to show".
Using v1.2024.6.1
When "which columns to show" setting is set to "in the query" (the default) and the Fetch XML query has no attribute tags (returning all columns), an ArgumentNullException is thrown when clicking the Add button. To workaround I had to add an attribute (or use a view), then click Add in order to get to the settings and select "everything" for "which columns to show".