That's false. For USA to be able to block exports of the technology, more than 25% (if I remember correctly) of parts has to be of US origin. When the EUV program started, the share of US technology was much higher, but as the program progressed, it was diluted.

USA could still block sale of EUV machines, by refusing export/licensing of critical components, but they'd have to change their laws first.

Fact is that ASML voluntarily chose to block exports to China. In part because they want to keep good relations with USA. It's the US that funded the EUV program in the beginning after all. But I'm sure ASML was tired of China copying their stuff too, so it probably wasn't hard to convince them.