Well, you have the words, but…
A stationary mass can be broken up such as to release EMR energy. As a stationary mass, it can do no work and thus has no energy. Mass and energy are NOT the same thing. Mass is a property of inertia and/or point of gravitational migration. That is not the same as “ability to do work”.
There is “potential energy” such as a voltage or a gravitational displacement which has the ability to do work only when released to do so. Thus a mass is a type of “potential energy” storage incapable of doing work until the inner EMR is released. The amount of work stored within a mass can be calculated by E=mc^2.
In all cases, the EMR is doing the “work”. Even gravitational migration is due to ultra-minuscule EMR. But EMR has no mass, no inertia (by concurrent definition of inertia). Energy doesn’t equal mass and mass doesn’t equal energy. Mass is a storage mechanism of energy that possesses inertia. Work is accomplished through EMR, void of mass/storage.