A search for pair production of bottom squarks in events with hadronically decaying τ-leptons, b-taggedjets, and large missing transverse momentum is presented. The analyzed dataset is based on proton-protoncollisions at ffiffiffisp¼13 TeV delivered by the Large Hadron Collider and recorded by the ATLAS detectorfrom 2015 to 2018, and corresponds to an integrated luminosity of 139 fb−1. The observed data arecompatible with the expected Standard Model background. Results are interpreted in a simplified modelwhere each bottom squark is assumed to decay into the second-lightest neutralino  ̃χ02 and a bottom quark,with  ̃χ02 decaying into a Higgs boson and the lightest neutralino  ̃χ01. The search focuses on final states whereat least one Higgs boson decays into a pair of hadronically decaying τ-leptons. This allows the acceptanceand thus the sensitivity to be significantly improved relative to the previous results at low masses of the  ̃χ02,where bottom-squark masses up to 850 GeV are excluded at the 95% confidence level, assuming a massdifference of 130 GeV between  ̃χ02 and  ̃χ01. Model-independent upper limits are also set on the cross sectionof processes beyond the Standard Model.