I discovered that Avast 22.12 kills Bank Mode in Avast Secure Browser. I then discovered that I had neglected to download a copy of Avast 22.11 offline installer. I therefore had to reinstall Avast 22.10 the offline installer of which I possess.
Why aren't earlier offline installers available? A cock-up over a new version surely justifies users being able to recover at least the previous Avast version offline installer.