Why are certain photos missing on my iPhone 16 in Denmark compared to YouTube?

Hard to say, based on so little information.

Perhaps the person who made the YouTube video is using a different model phone or a different operating system. (For example, I think the VIBRANT style shown in your screenshot is no longer available on certain models and systems levels.)

Perhaps they just didn't show you all the steps necessary to use the features you think you are missing. (For example, the eraser too only works in markup mode and only erase markups.)

Perhaps there is something about the photos you are working on that is preventing you from using those features. (For example, there are ways of placing a photo on a phone that will prevent it from being manipulated by the phone.)