Check out this solution Inappropriate MathJax rendering in AnkiMobile - #6 by anon15424829.
Edit: some tall math symbols were clipped using that solution so I added some padding. I also made the scrollbar thinner:
mjx-container {
overflow-x: scroll;
max-width: 100%;
padding: 5px;
}
mjx-container::-webkit-scrollbar {
height: 5px !important;
}
Edit2: apparently MathJax v4 has automatic line breaking. So this should be fixed along with Investigate MathJax 4.0 · Issue #4277 · ankitects/anki · GitHub.