After you updated angular to 9, you found that Material Components do not work. Well, you need update.

Steps:

1. Update Angular Material to version 8 by running ng update @angular/material@8 in your terminal.
2. Instead of importing from @angular/material, you should import deeply from the specific component. E.g. @angular/material/button. ng update will do this automatically for you.
3. Run ng update @angular/material.