I can't find the documentation for firebox upgrade path. We have firebox with version 12.0(build 540035) but what is the recommended upgrade path to latest version 12.7.2(build 655803)? Its consider quite a big jump.
The upgrade path is always in the Release Notes for the version to which you are trying to upgrade.
What actual model do you have?
If your firebox qualifies to install 11.7.2, then it must be a Firebox T20, T40, T55, T70, T80, M270, M290, M370, M390, M400, M440, M470, M500, M570, M590, M670, M690, M4600, M4800, M5600, M5800, FireboxV, or Firebox Cloud, and "the latest" firmware for those models is Fireware 12.8, released 17 March 2022.