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We present an application of the unitarity-based dispersion matrix (DM)approach to the extraction of the CKM matrix element $|V_{cb}|$ from theexperimental data on the exclusive semileptonic $B_{(s)} \to D_{(s)}^{(*)} \ell\nu_\ell$ decays. The DM method allows to achieve a non-perturbative,model-independent determination of the momentum dependence of the semileptonicform factors. Starting from lattice results available at large values of the4-momentum transfer and implementing non-perturbative unitarity bound, thebehaviour of the form factors in their whole kinematical range is obtainedwithout introducing any explicit parameterization of their momentum dependence.We consider the four exclusive semileptonic $B_{(s)} \to D_{(s)}^{(*)} \ell\nu_\ell$ decays and extract $|V_{cb}|$ from the experimental data for eachtransition. The average over the four channels is $|V_{cb}| = (41.2 \pm 0.8)\cdot 10^{-3} $, which is compatible with the latest inclusive determination at$1\sigma$ level. We address also the issue of Lepton Flavour Universality bycomputing pure theoretical estimates of the $\tau/\ell$ ratios of the branchingfractions for each channel, where $\ell$ is a light lepton. In the case of alight spectator quark we obtain $R(D^*) = 0.275(8)$ and $R(D) = 0.296(8)$,which are compatible with the corresponding experimental values within$1.3\sigma$. In the case of a strange spectator quark we obtain$\textit{R}(D_s^*) =0.2497(60)$ and $\textit{R}(D_s) = 0.298(5)$. The differentvalues for $R(D_s^*)$ and $R(D^*)$ may reflect $SU(3)_F$ symmetry breakingeffects, which seem to be present in some of the lattice form factors,especially at large values of the recoil.

$|V_{cb}|$, LFU and $SU(3)_F$ symmetry breaking in $B_{(s)} \to D_{(s)}^{(*)} \ell \nu_\ell$ decays using Lattice QCD and Unitarity