Correlated kagome metals host unique electronic states that enable exotic quantum phenomena. In the recently emerged ${\mathrm{CsCr}}_6{\mathrm{Sb}}_6$, these manifest through Kondo behavior from localized $\mathrm{Cr}\text{−}3d$ electrons and unprecedented band flattening near the Fermi level. Yet the intricate interplay among Kondo screening, magnetic frustration, and electronic correlations remains poorly understood—a fundamental gap we address through multifaceted experimental and theoretical approaches. Our angle-resolved photoemission spectroscopy measurements reveal electronic correlation-renormalized flat bands, and our muon spin relaxation study detects short-range magnetic order at $T_{\mathrm{N}}\sim 80\mathrm{K}$. Complementing these findings, density-functional theory and dynamical mean-field theory calculations identify a coherent-incoherent crossover at $T_{\mathrm{N}}$, with a remarkable restoration of coherence accompanying local moment suppression—an anomalous hallmark of Kondo behavior. Intriguingly, despite strong interlayer antiferromagnetic coupling, the system evades long-range magnetic order due to competing magnetic configurations separated by sub-meV energy differences. These insights establish ${\mathrm{CsCr}}_6{\mathrm{Sb}}_6$ as a prototypical platform for investigating dynamical Kondo screening in correlated flat-band systems, opening new avenues to study flat-band physics and frustrated magnetism in correlated kagome lattices.

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• Flat bands
• Kondo effect
• Magnetic order
• Topological materials