Although cards with MathJax content can render perfectly fine in Anki Desktop on macOS, when those cards are studied via AnkiWeb on a mobile device, the MathJax literally displays as “(z^{(l)}_j)”
I decided to switch to MathJax because the documentation says: “LaTeX . . . is only recommended for users that need more features than MathJax provides.” It also says: “MathJax is a browser-based typesetting system.” I am using Safari on iOS 13.