This is kind of pedantic, but to my understanding, even normal exothermic chemical reactions do convert mass to energy. It’s just that the amount of mass lost is extremely negligible. Conservation of mass is an oversimplification that is close enough to match any real world measurement you’d care about.

Nuclear reactions are when you start getting into doing mass-energy conversion at scale.

In much the same way that no electrical device actually "consumes energy" (conservation of energy).

Your power company still won't accept that perfectly correct explanation in lieu of payment.

Chemical reactions also lose mass according to E=mc^2, but m is so small that it's hard to notice.