Must Lay Arahants become Buddhist Monks? A lay person who becomes an Arahant must become a monk or they will die?

Can anyone explain what this teaching means?

Do they have to become a Buddhist Monk?

Can they just leave the world and become a hermit?

Could it be appropriate to just die and enter parinibbana?
If and when a lay-follower attains arahant-ship, he or she has to either enter the Order that very day or else must attain parinibbàna. This is a Dhammata. This is conformity to the Dhammaniyāma – a general rule in Dhamma.
This is discussed in the Milindapanha, which is a set of three Buddhist books that records the dialogues between the Indian monk Nagasena and the Indo-Greek king Milinda.

Milinda: &quot;You say that if a layman attains arahantship he must either enter the Order that very day or die and attain parinibbàna. Yet if he is unable to find a robe and bowl and preceptor then that exalted condition of arahantship is a waste, for destruction of life is involved in it.&quot;
Nagasena: &quot;The fault does not lie with arahantship but with the state of a layman, because it is too weak to support arahantship. Just as, O king, although food protects the life of beings it will take away the life of one whose digestion is weak; so too, if a layman attains arahantship he must, because of the weakness of that condition, enter the Order that very day or die.&quot;