It strikes me as a key area for humanities advancement on and off Earth but one that doesn’t have much backing.
I was thinking if someone theoretically had enough financial security to not have to worry about money again and was starting over from scratch, would it be possible?
If you wanted to be on the cutting edge as a fusion physicist, and let's imagine you are a bit rusty on calculus & physics, you'd probably be looking at >2yrs remedial math/physics classes at the undergrad level, plus about 6yrs of graduate work. If you're able to get into a big-name program, you could be doing something useful after the first couple years of the graduate program.
If you're a data analyst/engineering or programmer, you could probably get involved in a less direct way (supporting the science team) much faster.
Here's a pretty good list of (primarily US-based) jobs in the fusion sector, including both scientist & other roles. Have a look at the qualifications these roles require.
Don't assume that you can't contribute right now. Companies that work in fusion and they will need all the stuff that normal companies need. If you are a web developer, they likely have websites and will have web teams. If you are a UX designer they will likely have control systems that need to be designed.
If you're serious about this, I would seek out people in the industry and just talk to them about your interest and ask what kind of roles on their team would be a good match.
Being genuinely super passionate about the work of the company is a huge plus when you are interviewing. Don't undervalue your current skills and your enthusiasm.
It spans the gamut from "I'm going to read an article in the Times today" to "I'm going to complete a PhD in Nuclear Physics and then do a postdoc at a fusion lab."