You shouldn't need
@import "~bootstrap/dist/css/bootstrap.css";
or
<link rel="stylesheet" href="../node_modules/bootstrap/dist/css/bootstrap.css">
Putting bootstrap.css into angular.json > styles should be enough.
You should also initialize jQuery in app.component.ts
Because Bootstrap (still) uses jQuery, you should consider using something like primefaces.org/primeng It's based on Bootstrap (loosely) and doesn't require jQuery. Ie: using Bootstrap with Angular isn't ideal now a days.