to my knowledge memory scan is already part of the normal scan…so this is something extra. Never known exactly why it is there
when you get these detections, you will see that there is nothing you can do…as it is a process loaded in memory and not a file that you can quarantine / delete so the action button is grey

many users have played with those settings so you are not the first one to see this. remeber the avast guys have played with malware 24/7 for 20 years so there is a reason why the default settings are as they are
detection in memory is this forums second most asked question so plenty info if you forum search…
nr 1 asked is files that cant be scanned https://blog.avast.com/2014/02/28/how-do-i-handle-files-that-avast-cant-scan/