Lepton flavour universality tests in $b \to c l \nu$ decays at the LHCb experiment

Semileptonic charged current $b \to c l^- \overline{\nu}_l$ decays offer a compelling avenue to probe the limits of the Standard Model and investigate lepton flavor universality (LFU). While the SM maintains flavor universality, new physics models can introduce interactions that violate this universality, particularly for decays involving third-generation quarks and leptons. An enticing observable to test LFU is the ratio of branching fractions of $b \to c \tau^- \overline{\nu}_\tau$ and $b \to c \mu^- \overline{\nu}_\mu$ decays. Recently, the LHCb experiment measured this ratio using $\overline{B} \to D^{(*)} l^- \overline{\nu}_l$ decays. We discuss these results in this proceedings of the 57th Rencontres de Moriond on Electroweak Interactions and Unified Theories.