@Cor-Slagmolen what PI is this on?
edit ~/MagicMirror/package.json
change this line
"start": "DISPLAY=\"${DISPLAY:=:0}\" ./node_modules/.bin/electron js/electron.js",to this
"start": "DISPLAY=\"${DISPLAY:=:0}\" ./node_modules/.bin/electron --disable-gpu js/electron.js",