It is due to configuration corruption.So docker engine cannot start.

my env : macOS Catalina, Intel chip, Docker Desktop 4.15.0

cd ~/.docker 
mv daemon.json daemon-old.json
vi daemon.json
    {"experimental":false,"builder":{"gc": 
    {"enabled":true,"defaultKeepStorage":"20GB"}},"features": 
    {"buildkit":true}}

Hope,it can help

enter image description here