Evolution of the [O III]+Hβ-to-UV ratio with M_UV for the 7 < z < 8 sample (left panel) and the 8 < z < 9 sample (right panel). In black is the FRESCO data from Meyer et al. (2024) with depth limit in dashed line, to cover the bright end. The dotted line shows the assumed evolution of the ratio following R = −0.1 ×  M_UV − 4.2, which enables us to flatten an nebular emission line LF from an intrinsically steep LF, as shown in Fig. 10. This law is arbitrary and chosen to follow the data in a simple manner. However, it does follow closely the linear fit of the data.