Supernova: The Best Quad Sudoku Ever

Today's sudoku leaves us speechless. It's called Supernova and it's by Nahileon. This is a crazy, extraordinary puzzle that will leave you shaking your head in admiration. Play the puzzle at the following link:

https://app.crackingthecryptic.com/sudoku/MF3rQB3Tgr

Rules:
Normal Sudoku rules apply. A digit in a circle must appear in at least one of the four cells surrounding that circle. Every even digit must see at least one identical digit via a knight's move (in chess). E.g. if r5c2 is a 2 then there must be at least one 2 in r3c1, r3c3, r4c4, r6c4, r7c3 and r7c1.