IncludeWithDefaultProperties will return all fields of list item

ListItemCollection listItems = list.GetItems(query);
context.Load(listItems, items => items.IncludeWithDefaultProperties(item => item.Id));
context.ExecuteQuery();

It seems IncludeWithDefaultProperties will return a list item with all columns.

So you can just do

ListItemCollection listItems = list.GetItems(query);
context.Load(listItems, items => items.IncludeWithDefaultProperties());
context.ExecuteQuery();