setMainToolbarNavigationIcon

Sets the main toolbar's navigation (up / back) icon and its accessibility label, or null to remove the affordance — the Compose counterpart of the AppCompat Toolbar.setNavigationIcon. The SDK's own toolbar renders it at the leading edge through com.pspdfkit.compose.toolbar.composables.NutrientMainToolbarNavigationIcon, the default navigationIcon slot of com.pspdfkit.compose.toolbar.composables.NutrientMainToolbar; a tap arrives as ToolbarAction.NavigationClicked (see addNavigationClickHandler).

A Compose host composing its own navigationIcon slot does not need this: the slot wins.