  Asymptotically safe quantum gravity is an approach to quantum gravity that
achieves formulates a standard quantum field theory for the metric. Therefore,
even the deep quantum gravity regime, that is expected to determine the true
structure of the core of black holes, is described by a spacetime metric. The
essence of asymptotic safety lies in a new symmetry of the theory -- quantum
scale symmetry -- which characterizes the short-distance regime of quantum
gravity. It implies the absence of physical scales. Therefore, the Newton
coupling, which corresponds to a scale, namely the Planck length, must vanish
asymptotically in the short-distance regime. This implies a weakening of the
gravitational interaction, from which a resolution of classical spacetime
singularities can be expected. In practise, properties of black holes in
asymptotically safe quantum gravity cannot yet be derived from first
principles, but are constructed using a heuristic procedure known as
Renormalization Group improvement. The resulting asymptotic-safety inspired
black holes have been constructed both for vanishing and for nonvanishing spin
parameter. They are characterized by (i) the absence of curvature
singularities, (ii) a more compact event horizon and photon sphere, (iii) a
second (inner) horizon even at vanishing spin and (iv) a cold remnant as a
possible final product of the Hawking evaporation. Observations can start to
constrain the quantum-gravity scale that can be treated as a free parameter in
asymptotic-safety inspired black holes. For slowly-spinning black holes,
constraints from the EHT and X-ray observations can only constrain
quantum-gravity scales far above the Planck length. In the limit of
near-critical spin, asymptotic-safety inspired black holes may ``light up" in a
way the ngEHT may be sensitive to, even for a quantum-gravity scale equalling
the Planck length.
