Sometimes your UI will just not scale for large text sizes. Simple changes, for large sizes, like disposing elements vertically instead of horizontally, reducing the number of columns, and allowing more lines of text, can do the trick most times.

Calendar of Advent iOS Accessibility. Day 23. Adapt your UI. Example of Apple's Stock app. The first one has the default text size. The second one uses the largest possible text size. In the first one, the symbol and name are at the left of its row, there is a small graph in the middle, and the value and percentage change to the right. In the second one, the symbol, name, value, and percentage change are at the left, taking most of the row width, and the only thing to the right is the graph. That gives plenty more horizontal space for the text.