  A search is presented for new particles produced at the LHC in proton-proton
collisions at $\sqrt{s} =$ 13 TeV, using events with energetic jets and large
missing transverse momentum. The analysis is based on a data sample
corresponding to an integrated luminosity of 101 fb$^{-1}$, collected in
2017-2018 with the CMS detector. Machine learning techniques are used to define
separate categories for events with narrow jets from initial-state radiation
and events with large-radius jets consistent with a hadronic decay of a W or Z
boson. A statistical combination is made with an earlier search based on a data
sample of 36 fb$^{-1}$, collected in 2016. No significant excess of events is
observed with respect to the standard model background expectation determined
from control samples in data. The results are interpreted in terms of limits on
the branching fraction of an invisible decay of the Higgs boson, as well as
constraints on simplified models of dark matter, on first-generation scalar
leptoquarks decaying to quarks and neutrinos, and on models with large extra
dimensions. Several of the new limits, specifically for spin-1 dark matter
mediators, pseudoscalar mediators, colored mediators, and leptoquarks, are the
most restrictive to date.
