Should I edit the code of old GitHub repositories(from 2 years) make it clean and replace old technologies with new ones like xml and compose or create a new repository of the same app but with new technologies or create new branch??

I'd vote for updating the old repos: People have it starred or bookmarked and will find it more easily. Also, the Git history makes it clear what updates happened. And it's nice to have a repo maintained for a longer time.

I also prefer to update old repos. I kinda like how my https://github.com/StefanOltmann/Kaesekaestchen is 8 years old now. 😄

+1 for keep the same repository. If you ever want to do a talk, blog post etc about the migration it'll be really handy to have the commits showing the diff for each change