Create a screen locker for cordova/bootstrap5 mobile app

Hi
i would like to create a sort of “locked screen” in my app.
I created a bootstrap modal full page, no close on click with a form to provide password to unlock.
This works well but when I click on android device back button, the modal hides.
How can I disable back button when the modal “locked screen” is shown ?
If it’s not possible what should be an alternative ?
Thanks.