I'm not an expert at all, but I follow news about fusion energy with keen interest. Getting to conditions where fusion reactions can take place requires modeling the physics with supercomputers. I think the physicists have a handle on the software required to do that modeling; they also have access to the computers.
I think if you have a software background and want to contribute, you should consider applying for a job with one of the projects themselves. General Atomics lists 135 software jobs (https://www.ga-careers.com/search-jobs/software/499/1) for instance.