There are plenty of free lunches, they're called externalities, free rider problems, etc., etc.
For a maxim held by so many who flirt with economics, it's strange that so much of the field is explicitly about determining where the free lunches are.
The point of TANSTAAFL isn't that you'll never eat for free. It's that someone pays for your lunch. In an externality, someone pays for your lunch involuntarily.
And I don't think that makes it any more relevant as a maxim here. Social safety nets, welfare, and UBI are all giving lunches to people. Sometimes they produce net benefits, sometimes not.
Throwing in TANSTAAFL doesn't add anything to the discussion.
UBI represents a massive increase in the level of redistribution proposed, so it's important to remember that it is redistribution and the money will have to come from somewhere.
The point is that every lunch is non-free to some people, even if it is free to others.
You might thing it trite or a truism, but very many people forget that the billions/trillions for UBI is going to be very expensive for a lot of people.
For a maxim held by so many who flirt with economics, it's strange that so much of the field is explicitly about determining where the free lunches are.