There is an apple in one of the three opaque boxes, a pear in the other, a plum in the third

There is an apple in one of the three opaque boxes, a pear in the other, a plum in the third, there are inscriptions on the boxes, but they are all false, what is in each of the boxes?

Let’s start solving the problem in order.

Let the inscription “pear not here” be on the first box. Therefore, here is a pear, since the condition says that the inscription on the box is incorrect.

Let’s also assume that the second box is labeled “here is an apple”. This means that there will be either a pear or a plum, but since the pear is already in the first box, hence there is a plum.

Then it remains that there is an apple in the third box with the inscription “here a plum”, because we have already put the pear in the first box, but there are no plums in this box.