Gunpowder does not exist in Minecraft Xbox 360 Edition.
It was added in the 1.0 "Release" update (Nov 2011) — **after** 4J Studios ceased updating the Xbox 360 Edition (final update TU73, 2018, equivalent to Java 1.12/1.13). The 360 codebase never received the 1.0 features.
The 360 Edition is a time capsule. Enjoy its frozen charm—or move to a living version.