This work presents the reinterpretation of the search for final states with at least one energetic jet and missing transverse momentum in the context of dark sector models with long-lived neutral particles. Results are based on $139 \mathrm{fb} ^{-1}$ of data collected in $pp$ collisions at $\sqrt{s} = 13 \mathrm{TeV}$ by the
ATLAS experiment during Run-2 at LHC. Decays of the Standard Model Higgs boson and of a new neutral heavy scalar mediator into long-lived particles are investigated in different channels. The resulting constraints generally extend those from dedicated searches at large proper lifetimes.