Enabling thermal dark matter within the vanilla <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mrow> <mml:msub> <mml:mrow> <mml:mi>L</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>μ</mml:mi> </mml:mrow> </mml:msub> <mml:mo>−

Thermal dark matter is a compelling setup that has been probed by a multitude of experiments, mostly in the GeV–TeV mass range. The thermal paradigm in the sub-GeV range is about to experience the same experimental test with the next generation of low-energy accelerators and light dark matter detectors. Motivated by this, we investigate thermal dark matter in the <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"> <a:msub> <a:mi>L</a:mi> <a:mi>μ</a:mi> </a:msub> <a:mo>−</a:mo> <a:msub> <a:mi>L</a:mi> <a:mi>τ</a:mi> </a:msub> </a:math> and assess how the introduction of a matter-dominated era impacts the parameter that yields the correct relic density. Interestingly, we show that the projected experiments, such as the Muon (Synchrotron) Ion Collider, Future Circular Collider-ee, and Light Dark Matter eXperiment, will probe a large region of the viable parameter space that yields the correct relic density. In the GeV–TeV mass regime, the usual large-scale detectors push the sensitivity. Our work highlights the rich interplay between early-Universe dynamics, dark matter phenomenology, and the discovery potential of next-generation experiments.