As far as I’m aware, there are no surviving myths about Sobek, save for the Roman period Book of the Faiyum, which centred around Sobek-Ra and His journey through the sky. It’s very much Sobek-as-Ra in the Faiyum, and it is a fascinating text, from the snippets I’ve read about it. The book is as much a map of the Faiyum as it is a religious text. It has to explain the sun differently because it sits to the west of the Nile, and the sun rises and falls over the lake, not the Nile. So there’s some fascinating concepts and imagery that I would love to explore more deeply, including Nit as a hippopotamus, protecting Sobek as a crocodile on Her back.
But this is a hard text to study, simply because hardly anyone publishes any research on it (in an accessible-to-me way), and a full translation in English is nowhere to be found. So most of what I know about this text comes from a 51 page article by Horst Beinlich, which seems to have been part of a larger book I can’t find anywhere, that breaks down the text and describes each of the sections and what they contain. What’s in that article from 2013 is literally all I know, and all my google-fu can turn up.