You’re welcome; just to let you know today I got the first ‘new version’ since this thread.
Once again I was unable to click on the on screen message, but this time I right clicked the avast icon, left clicked programme update and have downloaded it that way, with an apparently successful restart.

I have an unrelated quick question. I live alone and my main computer’s avast will be due for renewal in September but I am away for several weeks; can I renew before it is formally due? Thanks.