Personally I wouldn't call it a threat, but a notice if you haven't logged into your my.avast.com account for some time.
There are several topics relating to this, here is just one, that has had many replies,
https://forum.avast.com/index.php?topic=226661.0.
As I mentioned in that topic (Reply #3), this is poorly worded and may be considered a risk in these days of scams/phishing emails.
Even more so, some of the reason to actually access the my.avast.com site are being discontinued (the ability to monitor devices for each system you have avast installed on or people that you look after, family etc. See
Changes to device section of my.avast.com.
This makes the my.avast.com account virtually redundant for those using avast free, so why this bloody email, I just don't understand the mentality of such decisions.
To actually log on to the avast forum, your log on is indirectly linked the your my.avast.com account for validation. I would have thought that would suffice, that or the fact having an active avast installation, being updated VPS, program updates, etc. should be confirmation enough.