The fate of quantum entanglement at finite-temperature phase transitions remains an open question, particularly for continuous symmetry breaking where zero-temperature Goldstone modes generate long-range correlations. Using large-scale quantum Monte Carlo simulations, we investigate the third Rényi negativity across the $O\left(3\right)$ transition in the three-dimensional Heisenberg antiferromagnet, studying a thermal critical point with continuous symmetry. We uncover two fundamental results. First, the negativity exhibits a pure area law at the critical point, with the subleading constant term vanishing within statistical uncertainty. This demonstrates that thermal fluctuations completely destroy the long-range entanglement present at zero temperature. The divergent classical correlation length leaves no imprint on such quantum entanglement. Second, despite this absence of singular behavior in the negativity, its temperature derivative follows the exact scaling of the specific heat, yielding critical exponents $-\alpha /\nu \approx 0.190$ and $1/\nu \approx 1.350$ in precise agreement with the $O\left(3\right)$ universality class. Our work establishes that while quantum entanglement is blind to thermal criticality its thermodynamic derivatives encode the full universal scaling, revealing an unexpected connection between entanglement and classical phase transitions.

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• Continuous phase transition
• Critical phenomena
• Entanglement entropy
• Quantum Monte Carlo