This is in addition to Sodernaut's online cheese method.
Having read their guide on the cloud save not immediately updating, I trialed the following and found it to work:
- Select New Game and play as usual.
- Whenever you see the save symbol appear in the bottom right corner in a clean run, exit to main menu, go to home and quit the game. By quitting the game, the cloud save will update immediately with a clean run to that save point.
-Reload and contine playing. If you make a mistake/die/take too long, go straight to home, manage game and delete local save. DO NOT QUIT THE GAME (as it'll override your clean run). This will then reload your previous clean save when it downloads from the cloud.
Bear in mind, this adds quite a bit of time because of loading screens, but if, like me, you have distractions (children...) so can't continuously practice for one clean run in one go, I found this method worked well to chip away over time.