A Mott insulator can lose its gap yet refuse to metallize. In the spin–orbit-entangled iridate $\mathrm{S}{\mathrm{r}}_3\mathrm{I}{\mathrm{r}}_2{\mathrm{O}}_7$, transport reveals an abrupt collapse of the effective activation gap (${\mathrm{\Delta }}_{\mathrm{eff}}$) from $\sim 0.1–0.2$ eV to ≲0.02 eV within 12–17 GPa, yet $R$($T$) remains nonmetallic down to 2.6 K. Above this window, the low-temperature conduction follows three-dimensional Mott variable-range hopping with a strongly reduced hopping scale $T_0$. A concurrent magnetoresistance sign reversal further characterizes the postcollapse localized regime, with possible contributions from spin-related scattering. Helium-medium x-ray diffraction shows no resolvable symmetry change, supporting a Mott-Anderson crossover picture where localization preempts metallization. This disorder-inclusive framework may apply broadly to bandwidth-tuned correlated systems where quenched disorder coexists with a pressure-suppressed correlation gap.

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• Anderson localization
• High-pressure studies
• Metal-insulator transition
• Iridates
• Mott insulators
• Strongly correlated systems
• Electrical transport techniques
• Magnetoresistance
• X-ray diffraction