Is there any analytical formula that relates the longitudinal deformations to the transverse deformations of a cantilevered beam subjected to a transverse applied load?
If you are asking about geometrically non-linear bending of beams, including cantilever beams, there are several good publications including both closed-form analytical solutions and FEA implementations. For analytical solutions, there is a classical book by E.P. Popov “Nonlinear Problems …” but not sure if there is an English translation. For FEA implementations, you can just run nonlinear statements with large deformations, e.g., *NGEOM in Abaqus, and check relevant examples in corresponding codes.