False. There's lots of side-by-side recordings of Denuvo and non-Denuvo versions of games on YouTube clearly showing that Denuvo does impact performance.
No there aren't, because having identical builds of games with Denuvo actually removed and present is vanishingly rare.
If you compare a game that's had significant performance patches over a period of years and had Denuvo removed to the launch version (as so many of these videos are) then no shit you see performance differences, but it doesn't tell you anything.
Should be noted that even scene cracks don't fully remove denuvo and all the performance intense checks so the impact should be even larger on actually denuvo free versions.