In nuclear reactions, such as fission, the released energy is from the binding energy originally holding the nucleus together. Mass-energy total is conserved.
In other interesting events, such as pair-production where a photon whose energy is above 1.022 MeV generates a pair of massive particles (negative-charge electron and positive positron, each 0.511 MeV/c2), another object (a nearby heavy nucleus) must join into the event to conserve momentum while gaining a small amount of kinetic energy (recoil).
Yes indeed these follow the structure and setup of the first law where changes are just a matter of shifting existing energy form one box to another.
But there are many more fundamental processes where this is not the case.
For instance the photons in pair production above follows the
E = pc rule
Virtual photons do not.
These are examples of effect that lie at the foundation of QM which is driven by the Principle of Least Energy.
QM allows a system to 'borrow' energy from outside the system - which may be a vacuum or nowhere at all, in order to overcome an energy barrier allowing reconfiguration to a lower energy state.
Virtual particles, the formation of Cooper pairs in superconductivity, the formation of Higgs bosons (and thus mass) are micro examples,
There are many examples of this in chemistry, resonance of the benzene molecule, delocalising the bonds being one of them.