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We present a new investigation of the intergalactic medium near reionization using dark gaps in the Ly β forest. With its lower optical depth, Ly β offers a potentially more sensitive probe to any remaining neutral gas compared to the commonly used Ly α line. We identify dark gaps in the Ly β forest using spectra of 42 QSOs at z em > 5.5, including new data from the XQR-30 VLT Large Programme. Approximately 40% of these QSO spectra exhibit dark gaps longer than 10 h âˆ'1 Mpc at z ≃ 5.8. By comparing the results to predictions from simulations, we find that the data are broadly consistent both with models where fluctuations in the Ly α forest are caused solely by ionizing ultraviolet background fluctuations and with models that include large neutral hydrogen patches at z < 6 due to a late end to reionization. Of particular interest is a very long (L = 28 h âˆ'1 Mpc) and dark (Ď„ eff ≳ 6) gap persisting down to z ≃ 5.5 in the Ly β forest of the z = 5.85 QSO PSO J025âˆ'11. This gap may support late reionization models with a volume-weighted average neutral hydrogen fraction of 〈 x H I〉 ≳ 5% by z = 5.6. Finally, we infer constraints on 〈 x H I〉 over 5.5 ≲ z ≲ 6.0 based on the observed Ly β dark gap length distribution and a conservative relationship between gap length and neutral fraction derived from simulations. We find 〈 x H I〉 ≤ 0.05, 0.17, and 0.29 at z ≃ 5.55, 5.75, and 5.95, respectively. These constraints are consistent with models where reionization ends significantly later than z = 6. [ABSTRACT FROM AUTHOR]