The previous settings disappeared with the update of the user interface to version 1.0.512
In order to make some changes in the previous Settings I followed this procedure:
I reinstalled Avast with the offline installation file, downloaded as soon as the new version 20.3.2405 was released, by disabling the internet connection;
the old Settings were still present in the Settings-Troubleshooting menu and therefore I was able to access them by making the changes that interested me (at the end I also made a backup of the Settings);
I reactivated the internet and, as we wanted to demonstrate, with the update of the user interface from version 1.0.506 (it seems to me) to 1.0.512 the old Settings are gone.
It is clear that I can no longer access it, but what I needed I did.
Unfortunately, I don't think that after importing the saved Settings, it can reactivate the changes made because the wrong policy was to abolish access to the previous Settings and, unfortunately, I believe that this will also be the case in subsequent versions of Avast.
Then after each release of a new version there are serious drawbacks, that the times of switching off and switching on the PC have doubled in the latest versions, etc. .. it seems that it does not interest much.
They lived happily ever after having removed access to the previous Settings!!