Actually, I think I get it now. Thanks.
There is a way to do something similar in v23.05.14. But sadly there is a problem with the keyframes of that filter at the moment (reported here).
You can control the reveal of individual parts of the image. All of it on one track.
Preview:
My method of revealing the parts of the image is different than yours (fade-in, fade-out) but I think it looks as good 
Exported video: