I tried a few techniques, in terms of accessibility I think "old" ways are the best here.
<div class=flowchart>... crazy modern shit ...</div>
<ol class=sr-only>
<li id=step1> Water on stove.
<ol>
<li>Boiling? Proceed to <a href=#step2>Step 2</a></li>
<li>Otherwise return to <a href=#step1>Step 1</a></li>
</ol>
</li>
<li id=step2> Cook dumplings in water. Wait a minute.
Floating? Proceed to <a href=#step4>Step 4</a>.</li>
Otherwise proceed to <a href=#step3>Step 3</a>.</li>
</li>
<li id=step3> Stir dumplings. Return to <a href=#step2>Step 2</a>.</li>
...
</ol>
(or start with the anchors/list, and progressively enhance)