[Cin] Source=ProRes; render=low quality

Hi, To make a video, I recorded the screen as mkv/h264; then I encoded it as prores as intermediate and finally I rendered the project as mp4/x265. The parts of the project that are not derived from Prores look good; those that concern Prores are darker and above all of poor quality and illegible writing. Can you tell me why? https://streamable.com/x3ay1r