I certainly wouldn't consider this as an ad
it's not... it's just release notes like so many other programs (whether free or paid) do after an update.
In your case (rocksteady), it may have been delayed because of a problem accessing the avast server right after your computer was started.
I see this after every program update and restart
that's right for me too and I don't understand why some people discover it now unless it's the first time they update avast.

(But I don't think this is your case, you are not young here.)
This popup always appears (only once) after an update both in auto and manual mode
nb:However a few months ago, there was a bug with this popup... it appeared at each startup and that was not normal.