What other effect besides travel restrictions would effect housing supply as quickly as in a month?

I suppose that no landlord would have been able to kick out a tenant short on a month of rent in Ireland.

Hmmmm, what else changed in that period... I can't think of anything. Other than airbnb's drying up, my life is about the same as it was a few months ago. There are so many things that have changed in that period, it's nearly impossible to make a strong argument that any one change caused any one other change. In stats speak, the exclusion restriction you'd usually require for this kind of statement is not valid here.

For starters, a bunch of people losing their jobs would give up their highly-priced city rental that was close to work.

Not everyone actually wants to pay the premium for city life, and once the job doesn't tie them there they can quickly leave.

Many of the shelter-in-place orders have banned anything not essential, like groceries or other supplies. That includes moving.

How did the supply dry up so fast when no one is to leave their houses? It has to be AirBnB/travel bans; even the 2008 housing bubble 'asplosion didn't move that fast.

The 2008 collapse didn't leave nearly so many jobless. I assume you've seen the unprecedented unemployment claim charts? https://www.cnn.com/2020/04/02/economy/unemployment-benefits...

It's all beside the point. You'd have to refute literally every single other possible cause to establish that airbnb was the culprit here.