  Differential cross-sections for top-quark pair production, inclusively and in
association with jets, are measured in $pp$ collisions at a centre-of-mass
energy of 13 TeV with the ATLAS detector at the LHC using an integrated
luminosity of 140 fb$^{-1}$. The events are selected with one charged lepton
(electron or muon) and at least four jets. The differential cross-sections are
presented at particle level as functions of several jet observables, including
angular correlations, jet transverse momenta and invariant masses of the jets
in the final state, which characterise the kinematics and dynamics of the
top-antitop system and the hard QCD radiation in the system with associated
jets. The typical precision is 5%-15% for the absolute differential
cross-sections and 2%-4% for the normalised differential cross-sections.
Next-to-leading-order and next-to-next-to-leading-order QCD predictions are
found to provide an adequate description of the rate and shape of the
jet-angular observables. The description of the transverse momentum and
invariant mass observables is improved when next-to-next-to-leading-order QCD
corrections are included.
