Best-matching BH* model and blackbody fit to the optical spectrum. We matched the gray shaded wavelengths to the larger model grid presented in Naidu et al. (2025). We also show the blackbody that best fits the rest-frame optical (dashed blue) and UV (dashed purple), for which we obtain an effective temperature of T_BB, opt = 5753 K (fit to wavelengths highlighted with a gray shade) and T_BB, opt = 15 530 K (purple shade), respectively. For illustration, we also include the SED fit to the object ALT-31334 (z = 5.66; M_* = 10⁸ M_⊙), a typical compact blue galaxy that could resemble a hypothetical host for GN-9771 (see Sect. 6.1).