I agree that Goods still have to be produced. I didn't say UBI is a substitute for economic activity. I didn't say UBI was all that you need. You are attacking a straw man here.
To expand a bit more, UBI might help service workers and others other hourly wage workers to take care of themselves. The service workers are the people who interact with other people the most, so an infected service worker who doesn't have an option but to work will end up spreading the disease. UBI might be the answer to temporarily keep them alive.
All of us have to live on reserves if there's a shutdown. Just like China did. It is not going to be great. But the alternative is much worse. And I am not claiming this is a permanent solution.
How will that help the people who don't have your magical ability to derive sustenance directly from bank balances?
UBI is not a substitute for economic activity. Goods still need to be produced. We need to deal with the outbreak without shutting the system down.