I have been a loyal Avast user for many years, primarily because it was the only antivirus I ever found with a boot time scan. It always found stuff that got by the other protections. I am not finding it in the new free version. Is boot time scan available in any new version of Avast?
It is in all versions.
https://www.avast.com/faq.php?article=AVKB132
It always found stuff that got by the other protectionsYou mean PUP ? PUP = Possible Unwanted Programs > pup detection is default off except for in boot scan
And if you often find PUP after running a bootscan i would try running Malwarebytes
support and FAQ > search and find > https://support.avast.com/support/home
Avast 2016: Running a Boot-time scan > https://www.avast.com/faq.php?article=AVKB132#artTitle
Boot time scan is something you use if you have a problem removing a infection, it is not meant to be used as a regular scanner
“It is scheduled to run only as needed, not on a regular basis”. That is different from It is not meant to be used as a regular scan. 
Thank you! I don’t know why I couldn’t find it but thanks to your reply, I now have. Boot time scan is the single most useful tool in war against viruses.
The most useful tool in preventing system infections is and always has been knowledge 