  Inclusive and differential fiducial cross sections of the Higgs boson are
measured in the $H \to ZZ^{*} \to 4\ell$ ($\ell = e,\mu$) decay channel. The
results are based on proton$-$proton collision data produced at the Large
Hadron Collider at a centre-of-mass energy of 13 TeV and recorded by the ATLAS
detector from 2015 to 2018, equivalent to an integrated luminosity of 139
fb$^{-1}$. The inclusive fiducial cross section for the $H \to ZZ^{*} \to
4\ell$ process is measured to be $\sigma_\mathrm{fid} = 3.28 \pm 0.32$ fb, in
agreement with the Standard Model prediction of $\sigma_\mathrm{fid, SM} = 3.41
\pm 0.18 $ fb. Differential fiducial cross sections are measured for a variety
of observables which are sensitive to the production and decay of the Higgs
boson. All measurements are in agreement with the Standard Model predictions.
The results are used to constrain anomalous Higgs boson interactions with
Standard Model particles.
