In 2016, the ALICE experiment observed that the ratio of strange to non-strange hadron yields increases with the charged-particle multiplicity at midrapidity, evolving smoothly across interaction systems and energies. The origin of this effect in small systems remains an open question. In this seminar, we will present the measurement of (multi-)strange hadron yields in proton--proton collisions at $\sqrt{s} = \rm 13~TeV$ as a function of the local charged-particle multiplicity in the pseudorapidity interval |𝜂|<0.5 and of the very-forward energy measured with the ALICE Zero-Degree Calorimeters. The latter provides information on the effective energy, i.e. the energy effectively available for particle production in the collision once the energy carried by the leading particles is subtracted from the centre-of-mass energy. The yields of ${\rm K}^{0}_{\rm{S}}$, $\Lambda+\overline{\Lambda}$, and $\Xi^{-}+\overline{\Xi}^{+}$ per charged-particle are measured exploiting a multi-differential approach to decouple the dependence on the local multiplicity and effective energy. The results presented in this seminar provide new insights into the interplay between global properties of the collision, such as the initial available energy in the event, and the locally produced final hadronic state connected to the charged-particle multiplicity at midrapidity. Notably, a strong increase of strange baryon production with effective energy is observed for fixed charged-particle multiplicity at midrapidity. These results are discussed within the context of existing phenomenological models of hadronisation implemented in different tunes of the PYTHIA 8 event generator.

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