This is false. Carousel links do not need to be AMP. To be in the carousel, however, you must be approved by Google News publisher center—AMP not required.
It was one of the reasons why I switched exclusively to Brave on mobile because they didn't serve AMP to that user agent, which meant that Google search results loaded faster (that 100KB of render-blocking JavaScript meant a LOT of time looking at empty pages on the subway) and weren't broken if you tried to share or save the URLs.
Testing just now, I see only AMP links in the carousel but there are queries where a non-AMP link has sufficient rank to be featured in the top stories section.