Certainly! The passive voice focuses on the action or the object rather than who or what is performing the action. If you want to emphasize that the backpack is missing, you can construct a sentence in passive voice like this:
"The backpack is missing."
In this sentence, the focus is on the backpack itself, highlighting the fact that it is not present. If you want to provide more context or detail, you could expand on it like this:
"The backpack was left behind and is now missing."
This still keeps the emphasis on the backpack while using the passive structure. Remember, in passive voice, the subject of the sentence (in this case, "the backpack") receives the action rather than doing the action.