  A search for R-parity violating supersymmetry in final states characterised
by high jet multiplicity, at least one isolated light lepton and either zero or
at least three $b$-tagged jets is presented. The search uses 139 fb$^{-1}$ of
$\sqrt{s} = 13$ TeV proton-proton collision data collected by the ATLAS
experiment during Run 2 of the Large Hadron Collider. The results are
interpreted in the context of R-parity-violating supersymmetry models that
feature gluino production, top-squark production, or electroweakino production.
The dominant sources of background are estimated using a data-driven model,
based on observables at medium jet multiplicity, to predict the $b$-tagged jet
multiplicity distribution at the higher jet multiplicities used in the search.
Machine learning techniques are used to reach sensitivity to electroweakino
production, extending the data-driven background estimation to the shape of the
machine learning discriminant. No significant excess over the Standard Model
expectation is observed and exclusion limits at the 95% confidence-level are
extracted, reaching as high as 2.4 TeV in gluino mass, 1.35 TeV in top-squark
mass, and 320 (365) GeV in higgsino (wino) mass.
