I have a thousands of this error after initial implementation nad typing in terminal ng serve my-app of and i can\'t resolve it. This is first time for me when i have problem li
Looks like you have recently installed flex-layout package. Try removing this package folder from your node_modules folder and reinstalling previous version of this package.
Recently (2 days before current date), angular released latest angular-cli version (v9.0.1) due to which many packages are updated to support this latest cli version. In your case you might have old cli version and when you installed this package it was downloaded for latest cli version by default. So try downgrading your package version. Worked for me atleast.
Also, dont forget to downgrade the version of your package in package.json file