  Many extensions of the Standard Model predict the production of dark matter
particles at the LHC. Sufficiently light dark matter particles may be produced
in decays of the Higgs boson that would appear invisible to the detector. This
Letter presents a statistical combination of searches for H $\rightarrow$
invisible decays where multiple production modes of the Standard Model Higgs
boson are considered. These searches are performed with the ATLAS detector
using 139 fb$^{-1}$ of proton-proton collisions at a centre-of-mass energy of
$\sqrt{s} =13$ TeV at the LHC. In combination with the results at $\sqrt{s} =7$
TeV and 8 TeV, an upper limit on the H $\rightarrow$ invisible branching ratio
of 0.107 (0.077) at the 95% confidence level is observed (expected). These
results are also interpreted in the context of models where the 125 GeV Higgs
boson acts as a portal to dark matter, and limits are set on the scattering
cross-section of weakly interacting massive particles and nucleons.
