SuiteCRM8 Creating Custom Frontend Extension in SuiteCRM8.7.1 But Not Working

I have checked the documentation guide of suitecrm 8 and followed the guide but those commands are not even running like these:
ng g app myExt --projectRoot=extensions/my-ext/app --routing=false --style=scss
this command is giving error : Error: Unknown argument: projectRoot

Can Someone Help me with this

I think it is --project-root , not --projectRoot. Can you please try this

ng g app myExt --project-root=extensions/my-ext/app --routing=false --style=scss