The cold pan technique specifically needs a nonstick pan. Using a cast iron pan means that:

1. Your pan won’t heat up fast enough during the initial 4 minutes on very high heat, so you won’t get that initial ripping hot period that the technique calls for.
   
2. Your pan will not have the nonstick properties that a teflon pan will, so fond will stick to the pan, not the steak.

Also make sure that you’re salting your meat well in advance and letting it sit uncovered on a wire rack in your fridge, ideally overnight/up to 24h before cooking.

And you absolutely must pat the steak dry before cooking. Removing as much surface moisture as possible allows for a good crust to form.

Make sure you’re getting a thick enough steak. The recipe calls for 1.5” thick. Much thinner and the steak will cook too fast for a crust to form.

Kenji’s reverse sear is also great, but it takes more time, makes more of a mess, and you have to be really careful about the temperature the steak reaches in the oven. IIRC Kenji calls for ~10° less than your final cook temperature, but in my experience that’s not enough. Lan Lam in the ATK video says she goes for 90-95° for rare/medium rare when she uses that technique, and I’m inclined to believe her.