An eternal problem that I also struggled with. I had to put '<-BACK' buttons on the page and place them appropriately on the page because people were giving back in the browser out of habit.
Michal, I am rapidly coming to the same conclusion.
I have been playing around with javascript of the form:
B4X:
//Event listener to detect user has taken BACK action
window.addEventListener('popstate', () => {
b4j_raiseEvent('${Passed_Instance_Name}_Redo', {'value': sps_deeplink_acc_guid});
});