The flaw isn't just in the fact that it wasn't universal (I didn't receive money, for example). It's also in the fact that most (nearly all?) of the people receiving money were receiving it in lieu of income, and in fact were disabled from obtaining income.

Tack that onto a snarled global supply chain, and it's very difficult to pull meaningful outcomes from the noise: did people increase luxury and discretionary purchases just because they could, or were they influenced by an early glut of staple food purchases? Did people increase discretionary spending to entertain children and compensate for a lack of time spent outdoors and socializing? Did they purchase more expensive foodgoods for similar reasons?

I am not a particular proponent of UBI. But I don't think we (meaning us laypeople on HN) are going to be able, from our vantage point, to draw a useful conclusion from the last 30 months' economic activity. It's simply too weird.

You could have received money, if you quit your job.

Right. Which is among the reasons why it isn’t UBI, and is an adjacent factor for why it’s a poor proxy for UBI research.

Except so many people did do exactly that. UBI enthusiasts are saying people won’t quit their jobs etc. if it isn’t universal and forever. But they did.

I don't know what a "UBI enthusiast" is, but I'm not it.

I'm not aware of anybody who claims that people won't quit their jobs if you (1) make them stay indoors and (2) give them money, and (3) invert the economy (justifiably!) for 6 months.

The claim that UBI advocates make is that UBI, when actually applied, is just a negative income tax. Alaska has one, and it doesn't make people quit their jobs.