it feels counterintuitive to me that US "average poverty" dropped more than 50 percent in covid, while european stayed absolutely untouched.

I felt the same. But I think the reason is similar to how your fuel economy is absolutely destroyed by sitting still. When you average in a speed of zero the calculation goes haywire.

People in the US are so close to financial disaster that in order to avert disaster the US had to heavily subsidize those out of work. Many people got healthcare and unemployment benefits that would not have been otherwise available. This meant money for zero hours of work. When you average in $1/0 hours it does crazy things to the graph.

The reality is: During Covid the US rapidly adopted similar safety nets to EU countries and, in effect, aligned with their levels of poverty. Once the emergency measures ended we snapped back to our previous, precarious, poverty level.

Just my theory.

How much of that could be the lack of real social nets in the US compared to Europe?

In addition, anecdotally, everyone I know in the EU that had a job pre covid has a job today. I can't say the same thing about folks in the US.

Politicians are judged by these metrics, so they all get gamed.

It is not counterintuitive at all, unless you misunderstand the income levels of the poor. Sending everyone $1400 massively increased the income of the poorest Americans.

Different responses to the COIVD shutdowns. The US government gave stimulus money directly to the people, for many bringing an increase to one's income during that period. The European response was focused more on helping people keep their jobs so their incomes remained stable.