First I'm still using avast 20.2 not the latest version (but I don't think this would have changed).
My only guess is that the Smart Scan is a collection of different scans and there isn't a generate a report file in Smart Scan Settings. I don't see any report file related to the Snart Scan in the C:\ProgramData\AVAST Software\Avast\report location.
The Smart Scan isn't even listed in the Settings > Protection, so there doesn't appear to be anywhere to generate a scan report.
If you look in the Settings > Protection > Virus Scans > Custom Scans, that has a section on the Smart Scan but it is woefully inadequate all it has is if you want to schedule it or not.