I was trying to describe the scenario that's happening.
1. Avast version X is released, https scanning works for the current version of the browser(s)
2. A new version of the browser is released - with internal changes that prevent Avast https scanning from working
3. Avast version X+1 is released, with updated code to make https scanning work again
There's no way to avoid that (it's happening because there's no "supported" way of scanning browser traffic, i.e. no API - so WebShield, and especially https scanning, has to rely on some internal stuff of the browsers).
So yes, Avast supports HTTPS scanning - by updating the code and releasing it as a new version.
In case you think that version 11 would somehow be updated... that's not possible, the versioning is linear. When version 11 was updated, after a few minor versions it became version 12. Then, after a few minor version, it became version 17... and now we're at version 20.3 We can't go back in time and release an update for version 11 - even if a specific problem was found affecting all versions 11 and later, the fix would be version 20.4 - with all the changes of the past few years.
In special cases it's possible to release emergency updates for a few versions back - but that is limited to small changes (which updating all the https support code for the latest browsers definitely would not be), and it certainly can't go back years old. I mean, we probably wouldn't be able to even compile those old versions, the tools have been updated many times since then. (I'm not even sure if version 11 had the emergency updater, for that matter.)
So I have to repeat again - the only way to stay as safe as possible is to use the latest versions of the program. If you stay on an older version, you are at risk that some features stop working (because of changes in 3rd party software, i.e. out of our control), the antivirus may not be effective against latest threats (of course the antivirus core responds to the latest development in the world of malware in each version - so older version may not be able to "see" some things), and you may be vulnerable to some security bugs in the antivirus itself (which again we fix once we learn them - and the fix is released as new versions).