In this work, we explore the quasinormal modes (QNMs) of the Bonanno-Reuter black hole, one of the first regular black hole metric suggested by the asymptotically safe gravity (ASG) program. The running parameter $\alpha$ is set to a positive value, the related running Newton coupling vanishes at high energies, fully achieving an ultraviolet fixed point and eliminating nonphysical UV divergences. This yields a singularity-free geometry. Hence, we focus on the resulting renormalization-group-improved Schwarzschild metric, which naturally produces an (anti–)de Sitter nonsingular core. On the basis of this background, we compute the QNM spectrum for scalar, electromagnetic, and gravitational perturbations by employing the spectral method (SM). This method, recognized for its enhanced precision compared to high-order WKB methods, allows the identification of fundamental modes, extensive collections of overtones, and purely imaginary overdamped modes that were entirely missed in previous analyses. These characteristics, resolved here for the first time in the Bonanno-Reuter black hole, underscore the crucial importance of high-precision spectral methods in investigating delicate signatures of black hole models inspired by quantum gravity.

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• Alternative gravity theories
• General relativity
• Particle astrophysics
• Quantum fields in curved spacetime