jrt-fs.jar builds identically if built on the exact same physical machine, but if for example it is built on an Intel architecture xLinux machine and then the same source on an AMD architecture machine, it is always different.
Eg.Diff of same jdk-19 source built on an Intel vs AMD:
anleonar@anleonar-mac Downloads % diff -r jdk1 jdk2
Binary files jdk1/jdk-19+14/jmods/java.base.jmod and jdk2/jdk-19+14/jmods/java.base.jmod differ
Binary files jdk1/jdk-19+14/lib/jrt-fs.jar and jdk2/jdk-19+14/lib/jrt-fs.jar differ
Binary files jdk1/jdk-19+14/lib/server/classes_nocoops.jsa and jdk2/jdk-19+14/lib/server/classes_nocoops.jsa differ
diff -r jdk1/jdk-19+14/release jdk2/jdk-19+14/release
15c15
< BUILD_INFO="OS: Linux Version: 5.8.0-34-generic"
---
> BUILD_INFO="OS: Linux Version: 5.8.0-43-generic"