What is a single adverb for how something is supposed to be + verb
Solution 1:
You could say, “This object is conventionally stacked,” and I think the most common interpretation would be “by convention, people stack this object”. (However, watch out for the alternative interpretation, “this object has been stacked in a manner that I judge to be conventional”.)
“Traditionally” can be used in somewhat the same way, although it is narrower in its connotations.