Posterior distribution of Horndeski parameters in the stable basis parametrised by ${\widehat{D}}_{\mathrm{kin}}$ and $\mathrm{\Delta }{\widehat{M}}_{\ast }^2$ for the combination of KiDS-Legacy, DESI DR2 BAO, eBOSS DR16 RSD, and Planck 2018 TTTEEE, low-ℓ TT, and low-ℓ EE datasets. The blue and green contours assume a w₀w_aCDM and ΛCDM background cosmology, respectively. The inner and outer contours of the marginalised posteriors correspond to the 68% and 95% credible intervals, respectively.