KvadrantJumpList
fun KvadrantJumpList(letters: List<String>, enabled: Set<String>, modifier: Modifier = Modifier, columns: Int = 4, onLetterClick: (String) -> Unit = {}, cyrillic: FontFamily? = null)
The grid of letters a long list jumps from: squares with a 2 px border, the letter at 36 sp SemiBold, and a letter with nothing behind it drawn in the inactive colour rather than hidden — so the alphabet keeps its shape and your thumb lands where it expects to.
The phone only offered this once a list was long enough to need it; MIN_GROUPS_FOR_JUMP_LIST is that threshold.