The first direct, model-independent measurement is presented of the modulus of the Cabibbo–Kobayashi–Maskawa (CKM) matrix elements (|\eta |{V}{\text{t}\text{b}}), (|\eta |{V}{\text{t}\text{d}}), and (|\eta |{V}{\text{t}\text{s}}), in final states enriched in single top quark t-channel events. The analysis uses proton-proton collision data from the LHC, collected during 2016 by the CMS experiment, at a centre-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 35.9 fb({-1}). Processes directly sensitive to these matrix elements are considered at both the production and decay vertices of the top quark. In the standard model hypothesis of CKM unitarity, a lower limit of (|\eta |{V}{\text{t}\text{b}}>0.970) is measured at the 95% confidence level. Several theories beyond the standard model are considered, and by releasing all constraints among the involved parameters, the values (|\eta |{V}{\text{t}\text{b}}=0.988±0.024), and (|\eta |{{V}{\text{t}\text{d}}}^{2}+|\eta |{{V}_{\text{t}\text{s}}}^{2}=0.06±0.06), where the uncertainties include both statistical and systematic components, are measured.