While we're talking about Downs maybe being a "generational" safety (Schottenheimer's words), the play in the Purdue game below at 14:33 of the 1st quarter is exactly why he's considered to have that potential.
This isn't a play that shows up in a box score as a TFL, sack or INT, statistically its just a run of the mill tackle. It's not something you'll see in a highlight reel because it's not flashy and didn't come at some sort of critical juncture in a game.
But if you take the time to watch actual full games of prospects this is one of the ones that will stick with you, because the intelligence and instincts he shows is truly next level.
You have 3 WR's lined up to the right of the QB, with a RB who motions out into the flat in that direction behind the WR's, everything about it is meant to look like a quick screen to the RB towards the perimeter with the WR's blocking, with the intention of getting the defense to flow quickly towards the sideline. What it really ends up being is basically misdirection with a middle screen back towards the middle of the field, to the inside/slot WR towards that side who fakes like he's going to block towards the outside then cuts back in.
Downs is the only defender that really reads it and when he takes the first step towards the inside/slot WR Sonny Styles and Caden Curry are still moving towards the sideline towards the fake motion. When Downs actually makes the tackle Styles and Curry are just starting to take their first steps back towards the middle of the field.
If you pause it at 12:15 of the video (14:29 on the game clock) you can see how well it's set up with multiple OL releasing downfield and no OSU defenders near the ball carrier except for Downs who navigates between the OL, stopping the WR for a short gain. If not for Downs reading it so quickly it's probably a 8-12 yard gain, instead it's only 1 yard.
That play more than anything shows the next level intelligence/instincts everybody praised him for, he basically sees things happening before most players.