Spin-strain interactions under hydrostatic pressure in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>α</mml:mi><mml:mtext>−</mml:mtext><mml:msub><mml:mi>RuCl</mml:mi><mml:mn>3</mml:mn></mml:msub></mml:mrow></mml:math>

We investigate the effects of hydrostatic pressure on <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"><a:mrow><a:mi>α</a:mi><a:mtext>−</a:mtext><a:msub><a:mi>RuCl</a:mi><a:mn>3</a:mn></a:msub></a:mrow></a:math>, a prototypical material for the Kitaev spin model on a honeycomb lattice with a possible spin-liquid ground state. Using ultrasound measurements at pressures up to 1.16 GPa, we reveal significant modifications of the acoustic properties and the <b:math xmlns:b="http://www.w3.org/1998/Math/MathML"><b:mrow><b:mi>H</b:mi><b:mtext>−</b:mtext><b:mi>T</b:mi></b:mrow></b:math> phase diagram of this material. Hydrostatic pressure suppresses the three-dimensional magnetic order and induces a dimerization transition at higher pressures. At low pressures, the sound attenuation exhibits a linear temperature dependence, while above 0.28 GPa, it becomes nearly temperature independent, suggesting a shift in the phonon scattering regime dominated by Majorana fermions. These findings provide new insights into spin-strain interactions in Kitaev magnets and deliver a detailed characterization of the <c:math xmlns:c="http://www.w3.org/1998/Math/MathML"><c:mrow><c:mi>H</c:mi><c:mtext>−</c:mtext><c:mi>T</c:mi></c:mrow></c:math> phase diagram of <d:math xmlns:d="http://www.w3.org/1998/Math/MathML"><d:mrow><d:mi>α</d:mi><d:mtext>−</d:mtext><d:msub><d:mi>RuCl</d:mi><d:mn>3</d:mn></d:msub></d:mrow></d:math> under hydrostatic pressure.