We are currently shipping flatpak-builder-1.2.2 in RHEL 9, and 1.2.3 is a small bug-fix release in the same stable series. It fixes two bugs.

We are shipping Git >= 2.38.1, since RHEL 9.2, which disables the file protocol by default due to CVE-2022-39253. This breaks builds with Git submodules:
https://github.com/flatpak/flatpak-builder/issues/495

Secondly there's a typo in the terminal title set during a build.

These are fixed in flatpak-builder-1.2.3:
https://github.com/flatpak/flatpak-builder/commit/1d3e9043a7c6f05d
https://github.com/flatpak/flatpak-builder/commit/c2ec158dc85731b8