angular 9 angular material is not a module code example
Example 1: @angular/material/index.d.ts
It is changed in updated version of angular i think.
To resolve this issue you need to downgrade the angular/material version
Try to update the angular material (@angular/material@7.3.2) of this version.
npm uninstall -g @angular/material
npm cache clean --force
npm install -g @angular/material@7
Example 2: File "..node_modules/@angular/material/index.d.ts' is not a module.ts(2306)
#import the individual modules, as Angular no longer support installeting from @angular/material