  It is well-known that dark matter (DM) direct detection experiments and the
LHC are complementary, since they probe physical processes occurring at
different energy scales. And yet, there are aspects of this complementarity
which are still not fully understood, or exploited. For example, what is the
impact that the discovery of DM at XENONnT would have on present and future
searches for DM in LHC final states involving a pair of hadronic jets? In this
work we investigate the impact of a XENONnT signal on the interpretation of
current dijet searches at the LHC, and on the prospects for dijet signal
discovery at the High-Luminosity (HL) LHC in the framework of simplified
models. Specifically, we focus on a general class of simplified models where DM
can have spin 0, 1/2 or 1, and interacts with quarks through the exchange of a
scalar, pseudo-scalar, vector, or pseudo-vector mediator. We find that
exclusion limits on the mediator's mass and its coupling to quarks from dijet
searches at the LHC are significantly affected by a signal at XENONnT, and that
$\mathcal{O}(100)$ signal events at XENONnT would drastically narrow the region
in the parameter space of simplified models where a dijet signal can be
discovered at $5\sigma$ C.L. at the HL-LHC.
