Function sync_radio_tab_index 

pub fn sync_radio_tab_index(
    store: Res<'_, PropertyStore>,
    radios: Query<'_, '_, (Entity, &RadioButton, &mut TabIndex, Option<&DocumentOrder>, Has<Disabled>)>,
)

Roving tabindex: exactly one member per group sits in the Tab chain: the selected member, else the first enabled one. Everyone else holds TabIndex(-1), which cycle_focus_on_tab skips, so Tab jumps over the group as a unit in both directions.