This has been a major issue for a while on my iPhone. It’s easy to reproduce as long as you have enough text highlighted.
Write a bunch of text in the editor
Highlight the text
Tap the gear icon in the editor
Try to select “Hide Details” or “Blur Spoiler” (two I use a lot that are supposed to wrap the highlighted text)
It should select the menu option with a single tap, but it just doesn’t work. You can also see the highlight coloring even after the gear menu is opened even though the text itself isn’t visible. It’s as if the highlight effect has a higher z-index than the gear menu, or something along those lines.
See the video below. You can’t actually seem my taps, but the parts where “Hide Details” is blue is when I tried to tap it.