error TS1086: An accessor cannot be declared in an ambient context in Angular 9

Adding skipLibCheck: true in compilerOptions inside tsconfig.json file fixed my issue.

"compilerOptions": {
   "skipLibCheck": true,
},

According to your package.json, you're using Angular 8.3, but you've imported angular/cdk v9. You can downgrade your angular/cdk version or you can upgrade your Angular version to v9 by running:

ng update @angular/core @angular/cli

That will update your local angular version to 9. Then, just to sync material, run: ng update @angular/material