I want to change the order of my images in 'Favourites' in photos

You cannot do it directly. The predefined albums are all having a predefined sort order.

But you can create your own "My Favourites" albums as a smart album. "File > New Smart Album: Photo is Favourite"

In this custom smart album you can change the sort order to keep the photos sorted by newest first or by title.

And if you create a standard album with all your favourites, you can drag them in any order you want.