Representative two-dimensional UMAP projections of observed and synthetic spectra from the 8800–8835 Å window, with T_eff color coded. Left panel: PHOENIX-ACES set used for DL training and the 282 CARMENES spectra (green). Right panel: subsample of 14 CARMENES M dwarfs with interferometric T_eff values shown in Table 1 (green triangles and labeled). Colored circles represent their closest interpolated best-fit PHOENIX model, using Schweitzer et al. (2019) parameter estimations as a reference.