You should take a look at my company. Heirloom Computing. Heirloom.cc We have migrated many mainframe application and millions of lines of cobol and pl1 into Java and deployed it into production on prem and into the cloud.
But is the conversion maintainable by a human? I’ve seen Fortran to C translators that end up encoding state transition machines that are impossible to read.
Don’t know about COBOL, but we recently threw some ancient RPG 3 programs into ChatGPT for conversion to both ‘plain English’ and PHP and it got pretty close - maybe 80-90%.
I work at a company with a large COBOL codebase and this has been mentioned in a few presentations about our modernization efforts.