The recent discovery of superconductivity in bilayer Ruddlesden-Popper nickelates under hydrostatic pressure and epitaxial strain has opened a new platform for studying correlated superconductivity. In this talk, I will present a many-body perspective on the normal-state electronic structure within cluster dynamical mean-field theory in combination with density-functional theory. We show how electronic correlations evolve differently under symmetric (pressure) and asymmetric (strain) structural perturbations, resulting in enhanced interlayer correlations and strong orbital-selective renormalizations. This framework provides a unified interpretation of several experimental observations including angle-resolved photoemission and transport, and offers insights into the nature of the underlying superconductivity.