This looks like Avast is using any opportunity to throw up the ad, click bait and running a scan seems to be the starter for ten. Even if you haven’t got the free cleanup component installed, so how would it determine you have a performance issue.

I followed it through to the point where it offered 30 free trial or 1year at £x per month. To be brutally honest the monthly rate is extortionate for what cleanup is purported to do. More so when you can get CCleaner (now Piriform is part of Avast Software) to do pretty much the same for free, unless Avast have plans for that.