You are mixing definitions. In the math of special relativity, the Poincaré group was realized by Wigner in 1939 to permit representation of particles in quantum theories with intrinsic angular momentum. Thus nothing need be "spinning" for such point-like particles to represent actual, conserved, angular momentum, $$\vec{S}$$.
Wigner, E P. On the unitary representations of the inhomogeneous Lorentz group. Ann. Math. 40:149-204, (1939).
The same Poincaré group is why the magnetic dipole momentum is close to 2 times the classically expected value ($$\vec{\mu} \approx -2.00231930436 \frac{|e|}{2 m_e} \vec{S}$$) while the details of how the electron quantum field and the electromagnetic quantum field couple are responsible (in currently accepted physical theory) for why the ratio is not exactly 2 but closer to $$2 + \frac{\alpha}{\pi}$$ with $$\alpha$$ being the famous fine structure constant of quantum electrodynamics.
An electron is defined (in QED and the standard model of particle physics) as an excitation of the quantum field that is characterized by spin-1/2, rest mass ~ 0.5 MeV and couples to the electromagnetic and weak boson fields as a lepton of charge -1. So it will always have an intrinsic angular momentum measured as +1/2 or -1/2 along any axis you might choose (in units of h/(2 π)).
This is OK.
My question is, can this electron be considered as 'stationary body' as Einstein considered a 'stationary body' in his paper at this link https://www.fourmilab.ch/etexts/einstein/E_mc2/e_mc2.pdf .
A quote for 'stationary body' from Einstein's paper for reference, is as follows: "Let there be a stationary body in the system (x, y, z), and let its energy— referred to the system (x, y, z) be E0. Let the energy of the body relative to the system (ξ, η, ζ) moving as above with the velocity v, be H0."