You're asking how Europe would pay for a large scale social program? I hope you don't live in the US my friend because if AI gets to a point where UBI is ever needed you better get comfortable sleeping outside.
Europe's finances are in dire straights under the heavy pensions and existing government spending. The US also has high debt, but has much lower taxes than the EU so can theoretically raise revenue if it really needs to, while Europe has little room for more taxation
In the context of an AI revolution influenced requirement for UBI, the political mobilization & effort required to sort the financial situation of Europe is exceedingly more attainable than the effort & mobilizations required to (A) passing a UBI bill, (B) raising taxes (lol c'mon), and (C) distributing said resources into a social safety net in the US that is not means-tested to hell and equally distributed and fought at every corner by corporate America.
We're the only developed western country on planet that doesn't have healthcare as a human right and you think our governments will pass a universal basic income?