The Coronagraph Instrument (CGI) flight software is a surprisingly massive at over 100,000 source lines of C++ code, which is significantly larger than typical JPL payloads. It is running on a a LEON4 (SPARC) processor on a radiation-hardened Frontgrade Gaisler GR740 board, using Wind River's VxWorks.

You can read all about it in the tech deep dive here https://workshop.ipac.caltech.edu/romancgi24/talks/Day2_Fluc...