halacha - Should separating pull apart Challah rolls be considered a forbidden act of completion?

I have heard many people state that using Challah* rolls that are baked in one unit to be pulled apart might be a problem for making Leḥem** Mishneh on Shabbath. In fact, there are rolls that are sold in my local supermarket that have a sticker on the outside of the bag that says something to the effect of, "Ask your rabbi about Lechem*** Mishneh."

I've heard some people state that, in fact, it is not a problem from that perspective, since the rolls are meant to be used separately.

My question, though, is that if the latter opinion is correct, wouldn't that make it an even bigger problem, namely completing the creation of some product, or does this not apply to food?

CYLOR, of course.