As James says, in theory there is now a specialised pathway from L4 through to the EFL as an AR. However no one has yet done this, as Level 4 specialisation was only recently introduced.
The more well worn path is from L3. As an L3 you start in a 'dual' capacity where you do both middles at Step 3/4 and also lines at Step 2 (National League North / South). It is possible (though very rare and hard) to achieve promotions as an AR in your first two seasons as an L3 and this would get you to be an EFL AR, via the National League.