I wouldn’t be unhappy with a simple “This email has been checked for viruses by Avast antivirus software” but a 200 character cryptic link like that worries me.
You didn’t say whether this is normal. Please confirm or deny.
You have to follow the path I gave from first opening the AvastUI (user interface) at the bottom is the settings option.
Change the settings in the AvastUI > Components > Mail Shield > Customise > Behaviour - General and uncheck the ‘Insert note into’ options.
Or to be clearer AvastUI > Settings > Components > Mail Shield > Customise > Behaviour - General and uncheck the ‘Insert note into’ options.
See extract from your image with the Settings marked