@genesis8bit Hi, you can found the 9.1 for the XRS on archive.org at this url:
https://archive.org/details/recalbox-rpi4_64_xrs9.1.img

I have faced the same problem, wonderedwhy my XRS wouldn't boot on the 9.2.3 PULSTAR ...
The version 9.1 was working fine and then i updated to 9.2.3 PULSTAR with no problems.