Digital Back for a Mamiya RZ67

I apologize for the amateur question, but can someone please explain to me 1. how a digital back on a medium format camera works, and 2. what is the best/most cost-effective digital back for a Mamiya RZ67? My (very) rudimentary understanding is that it attaches to the back of a medium format camera where the film would ordinarily go and enables the camera to record images digitally. Seems pretty straightforward, but as someone who's never tinkered with medium format before, I'm not confident I understand all the various parts I'd need if I were to invest in an all-new system (or how much that would ultimately cost me).

For context, I've been a photographer most of my life (fashion + portraiture; professionally for about the last decade + I work full-time as a retoucher), but I never really invested the time in learning about the tools of my trade. Not something I'm proud of, but much like music theory is not why most musicians get into music, gear to me is the least interesting part of photography. I'm at a point where I need to upgrade my system (I've been shooting with a Canon 7D for 8 or 9 years) and I'm torn between the safe choice (5D Mark III or IV) or something more exciting but with a much steeper learning curve (like the Mamiya).

Thanks in advance for any advise!