IIRC, Apple agreed to crack his phone after they were presented with a warrant, but the FBI demanded backdoors to all apple products, which they declined to provide. I may be wrong though.
Discussion
Apple was not a part of it. An Australian firm, Azimuth Security, helped hack into the device with a Lightning port exploit.
https://www.theverge.com/2021/4/14/22383957/fbi-san-bernadino-iphone-hack-shooting-investigation