• Single-phase stability in high-entropy perovskite ceramics is achieved only for RE = La, Nd, and Sm, with a centrosymmetric cubic structure (Pm¯3m).
• The Nd-substituted compound exhibits enhanced photoactivity in the 200–1000 nm range, while cationic disorder increases Urbach energy and reduces the indirect bandgap.
• Unexpected relaxor ferroelectric behavior is observed despite the centrosymmetric structure, attributed to polar nanoregions (PNRs) coexisting with non-polar regions.
• The slim polarization loops and relaxor characteristics make these RE-modified high-entropy ceramics promising for high-energy storage applications.