The fact that the top quark’s lifetime is smaller than its hadronization and depolarization timescales makes its production and decay kinematic properties an important probe of physical processes beyond the Standard Model (SM). The challenging analysis of the fully differential top-quark decay will probe the tWb vertex structure using single-top-quark events at a center-of-mass energy of 13 TeV at the LHC, using the full Run 2 dataset, with the ATLAS detector. Simultaneous measurement of the five generalized W boson helicity fractions and two phases, the polarisation in three orthogonal directions of the produced top quark as well as the t-channel production cross-section will be performed. This study is exceptional as it uses a novel model-independent framework proposed in EPJ C77 (2017) 200 and a large amount of data from proton-proton collisions of an integrated luminosity 139 fb-1. After measuring the relevant physical quantities previously mentioned, it will be possible to put stringent limits to EFT complex operators of the tWb vertex. The same measurement can be performed with early Run 3 data and constrain EFT parameters at a different energy scale. Deviations from expected values would provide hints of physics beyond the SM, and furthermore, complex values could imply that the top-quark decay has a CP-violating component.