Posterior distribution of Horndeski parameters in the stable basis parametrised by ${\widehat{D}}_{\mathrm{kin}}$ and $\mathrm{\Delta }{\widehat{M}}_{\ast }^2$ (left) and ${\widehat{D}}_{\mathrm{kin}}$ and ${\widehat{c}}_{\mathrm{s}}^2$ (right) for a fixed A_L = 1. Additionally, we show the posterior distribution of the derived value of the braiding term at z = 0, α_B, 0. The blue contour shows constraints from the combination of KiDS-Legacy, DESI DR2 BAO, eBOSS DR16 RSD, and Planck 2018 TTTEEE, low-ℓ TT, and low-ℓ EE datasets, while the green contour illustrates constraints from an analysis with Planck data only. For comparison, the black contour shows our fiducial constraints with free A_L for the combination of all probes. The inner and outer contours of the marginalised posteriors correspond to the 68% and 95% credible intervals, respectively.