Windows Defender and Avast are OK together…Just on an Avast Full scan or boot scan Avast does find a bunch of Windows Defender Files and depending on your settings could put them in Virus Chest therefore Disabling WD…Labels them as Pups I believe…I would put those files in the exclude list in Avast…The one reason I didn’t like Windows Defender is because I dread Microsoft Updates on a monthly Basis…Let alone weekly or daily…I am always cautious when those updates from Microsoft come monthly and think that something else might slide in with them…But that is a personal opinion…And just Me…
Cheers!!! and safe surfing!!!