"All US states, by contrast, have "opt-in" laws. Would switching to "opt out" make a big difference? International studies suggest not. Spain, which has presumed consent, is only slightly ahead of the US in the number of transplants relative to its population; France and Belgium, with similar legislation in place, have fewer transplants.
Wales is currently the only part of the UK with an opt-out system - England is due to follow suit later this year. But the Welsh did not see an increase in organ donations after it changed its law in 2015."
https://www.bbc.com/news/world-us-canada-51266959