  Measurements of Higgs boson production cross sections and couplings in events
where the Higgs boson decays into a pair of photons are reported. Events are
selected from a sample of proton-proton collisions at $\sqrt{s} =$ 13 TeV
collected by the CMS detector at the LHC from 2016 to 2018, corresponding to an
integrated luminosity of 137 fb$^{-1}$. Analysis categories enriched in Higgs
boson events produced via gluon fusion, vector boson fusion, vector boson
associated production, and production associated with top quarks are
constructed. The total Higgs boson signal strength, relative to the standard
model (SM) prediction, is measured to be 1.12 $\pm$ 0.09. Other properties of
the Higgs boson are measured, including SM signal strength modifiers,
production cross sections, and its couplings to other particles. These include
the most precise measurements of gluon fusion and vector boson fusion Higgs
boson production in several different kinematic regions, the first measurement
of Higgs boson production in association with a top quark pair in five regions
of the Higgs boson transverse momentum, and an upper limit on the rate of Higgs
boson production in association with a single top quark. All results are found
to be in agreement with the SM expectations.
