Function bevy::ui::ui_focus_system

pub fn ui_focus_system(
    state: Local<'_, State>,
    camera: Query<'_, '_, (&Camera, Option<&UiCameraConfig>), ()>,
    windows: Query<'_, '_, &Window, ()>,
    mouse_button_input: Res<'_, ButtonInput<MouseButton>>,
    touches_input: Res<'_, Touches>,
    ui_scale: Res<'_, UiScale>,
    ui_stack: Res<'_, UiStack>,
    node_query: Query<'_, '_, NodeQuery, ()>,
    primary_window: Query<'_, '_, Entity, With<PrimaryWindow>>
)

The system that sets Interaction for all UI elements based on the mouse cursor activity

Entities with a hidden ViewVisibility are always treated as released.