Difference Between SRAM SX eagle chain and SRAM NX eagle chain(12 speed)?
The NX chain is of slightly higher quality, so it will last longer and shift better. That's not relevant here though.
Yes, you need to shorten a new chain in most cases. The riveted pins increase the chain's strength, but do require a decent chain tool to punch out. Hold the new chain up beside the old chain, matching link to link, and break it at the same length/link count.