We describe an ongoing analysis performed with the CMS experiment, studying decays of the heavy flavor baryon $\Xi^{-}_b$. The main result is the measurement of the branching fraction of $\Xi^{-}_b \to \Xi^{-} \psi(2S)$ relative to the normalization channel $\Xi^{-}_b \to \Xi^{-} J/\psi$, achieved with improved precision compared to previous measurements. The previous measurement of this ratio was found to deviate from the trend observed in analogous $b$-meson decays, and with the full statistics available from Run 3, this analysis aims to test whether this deviation persists. The analysis is based on a sample of $pp$ collisions at $\sqrt{s} = 13.6~$TeV, collected during the 2022, 2023, 2024, and 2025 running periods of Run 3 of the LHC, corresponding to an integrated luminosity of 279~fb$^{-1}$. These are preliminary results and are subject to change.