A possible weapon from the Penrose process proposed by Roger Penrose. Use rotating black holes.
Using the ring-shaped singularity passing enormous kinetic energy to an object that has fallen into the black hole, energy is recovered or dissipated exponentially from the black hole.
Cover the periphery of the ergosphere with a mirror of mass about the size of an asteroid and shoot electromagnetic waves inside. The shot energy is bounced back with greater energy each time it passes through the ergosphere. This is called “superradiant scattering”.
In other words, energy continues to double and expand. If the energy obtained in this way is expelled, it will be a bomb that exceeds the supernovae.
The power of a bomb is worthy of Hypernova for a supermassive black hole. Astronomical areas can be destroyed, destroyed, and evaporated. The effect is on the whole galaxy.
If energy is used as a resource rather than a blast, Level III civilization can prosper for trillions of years.