  FeSe is a unique high-$T_c$ iron-based superconductor in which nematicity,
superconductivity, and magnetism are entangled with each other in the $P$-$T$
phase diagram. We performed $^{77}$Se-nuclear magnetic resonance measurements
under pressures of up to 3.9 GPa on 12% S-substituted FeSe, in which the
complex overlap between the nematicity and magnetism are resolved. A
pressure-induced Lifshitz transition was observed at 1.0 GPa as an anomaly of
the density of states and as double superconducting (SC) domes accompanied by
different types of antiferromagnetic (AF) fluctuations. The low-$T_{\rm c}$ SC
dome below 1 GPa is accompanied by strong AF fluctuations, whereas the
high-$T_{\rm c}$ SC dome develops above 1 GPa, where AF fluctuations are fairly
weak. These results suggest the importance of the $d_{xy}$ orbital and its
intra-orbital coupling for the high-$T_{\rm c}$ superconductivity.

Superconductivity