Same problem but I found a fix
I had the same high contrast problem. With great effort, I discovered it was only for the new videos made with HEVC or H.265 format, Apples new and improved compression system. I’m using an iPhone 13 pro max. Zoominator doesn’t appear to have been updated in over a year. The older H.264 style still works with Zoominator. So you need to convert your newer video to the older style. To see what your video is, open it from your camera roll, then swipe up to reveal the meta data. The way I figured it out is to upload it to another video app, then immediately save it again and use that version. I used the free video editing app called Videoshop. There are probably other apps that will do it too. iMovie doesn’t do that for me.