The first measurement of coherent ${\rm Y}$(1S) meson photoproduction off heavy nuclei is performed using ultraperipheral lead-lead collisions collected by the CMS experiment at a nucleon-nucleon center-of-mass energy of 5.02 TeV. The nuclear gluonic structure is probed at a nucleon momentum fraction of order $x$ $\sim$ 10${}^{-3}$, determined by the kinematics of the process. Owing to the large ${\rm Y}$(1S) mass, the measurement reaches the highest scale accessible so far through coherent vector-meson photoproduction, ${\mu }^2$ = 22.4 GeV${}^2$, where nonlinear quantum chromodynamics effects are expected to be minimal. In the ${\rm Y}$(1S) rapidity range $|y|$ $<$ 1, the ratio of the measured photoproduction cross section to a baseline model prediction that neglects nuclear effects is $S_{{\rm Y}\mathrm{\text{(1S)}}}$ = 0.25 $\pm$ 0.06 (stat) $\pm$ 0.02 (syst), thereby demonstrating nuclear suppression in this process. Expressed in terms of a nuclear gluon suppression factor, the result yields $R_g^{\mathrm{\text{Pb}}}$($x$ $\approx$ 10${}^{-3}$, ${\mu }^2$ = 22.4 GeV${}^2$) = 0.55 $\pm$ 0.12 (stat) $\pm$ 0.02 (syst). The measured $S_{$$\mathrm{1S}}$ is only slightly larger than the values previously reported for coherent $\varphi$ photoproduction, despite the probed ${\mu }^2$ differing by approximately two orders of magnitude.