Ternary diagram of the MCMC models for TOI-2196 b in scenario 1 (red), with the planet mass and the radius as input to the model, and in scenario 2 (blue), where also the stellar abundances are included. The mantle mass fraction (MMF) is defined as MMF= 1 − CMF − x_H/He where the latter parameter is the H/He mass fraction and CMF is the core mass fraction. The green circle and black square indicate the position of Earth and Mercury in the ternary diagram, respectively. The maximum CMF constrained by planet formation is limited by the black dashed line (see Sect. 4.3).