Here: https://github.com/scroll-tech/reth/blob/871daf2943df348ca51e9d6cbf73e68a4bbcbbfd/crates/scroll/chainspec/src/dev.rs#L23
The problem with using an outdated genesis with Feynman and/or GalileoV2 activated from genesis, is that the node will execute the special state transitions (bytecode and storage slot updates at block 1. This is inconsistent with l2geth, and might cause other issues depending on the testing scenario.