Background/Objectives: Quiet quitting (QQ) has become a prominent concept in healthcare workforce discourse, yet its meaning, measurement, and relevance to care delivery remain unclear. This theory-informed scoping review mapped recent evidence on QQ and related disengagement-related constructs among nurses, focusing on conceptualization, measurement, and associations with nursing performance, patient safety, quality of care, and missed nursing care. Methods: The review was guided by the Population–Concept–Context (PCC) framework and reported in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses Extension for Scoping Reviews (PRISMA-ScR). Web of Science, Scopus, PubMed, the Cochrane Library, and CINAHL were searched on 19 March 2026 for empirical, peer-reviewed, English-language studies involving nurses and published from 2022 onward. Eligible studies examined QQ or adjacent disengagement-related constructs in relation to nursing performance or care-delivery outcomes. Data were charted narratively and appraised using the Mixed Methods Appraisal Tool (MMAT). Results: Seven studies met the inclusion criteria; two examined QQ directly. Direct evidence conceptualized QQ as reduced discretionary effort within formal role boundaries and situated it within adverse workplace conditions. Adjacent evidence addressed low work engagement, reduced vigor, low-effort and engagement–burnout profiles, which in some studies were associated with poorer perceived quality of care, lower safety behavior, poorer performance, or more missed care. No included study directly examined QQ in relation to missed nursing care. Conclusions: QQ in nursing should be reframed from a workforce label into a care-delivery question. Establishing its clinical relevance will require direct testing of whether QQ is associated with missed nursing care, a link that has not yet been examined directly.