"Contango" refers to the futures market of an asset trading at a premium to the spot price.
This allows you to short the future while longing spot to generate an arbitrage APR.
Right now, SOL futures are trading at 2.5% premium.
If you used 40% margin (2.5x leverage) on the short and staked the long (6% APR) you'd be looking at 20% APR.
The reason I like this play is that it can handle relative size.
2) Aavethena
Right now, the Aave/Ethena play generates about 15% APR at 2x leverage and could handle the entire $10M if you wanted. Granted, it won't last forever, but for right now it's a great play.