Photon spheres, ISCOs, and zoom-whirl orbits around effective quantum-gravity black holes surrounded by quintessence

<jats:p>We study a black hole (BH) solution surrounded by a quintessence field (QF) in the framework of effective quantum gravity (EQG). The geometry carries a quantum correction (QC) parameter [Formula: see text] and the QF parameters [Formula: see text], and it supports a three-horizon structure set jointly by quantum effects and dark energy. We derive analytical expressions for the photon sphere and the shadow radius for several values of the state parameter [Formula: see text]. The QF enlarges the shadow while the QC shrinks it, so the two act against each other and the net shift may be observable. Using Event Horizon Telescope (EHT) data for M87*, we constrain the QC parameter and find that the allowed range of [Formula: see text] widens as [Formula: see text] grows. We then study null and time-like geodesics, showing how the QC bends photon paths and changes the energy, angular momentum, and stability of massive-particle orbits. The analysis is extended to periodic zoom-whirl orbits; quintessence admits such orbits at lower energies than the purely quantum-corrected case. Scalar perturbations and their effective potentials are computed to show how the QC and QF together shape the BH response. Across the observables examined, the QC and the QF often pull in opposite directions, which offers a way to test quantum-gravity proposals and dark energy models together through future high-precision astronomical observations.</jats:p>