After update Popper.js problem · Issue #4249 · ng-bootstrap/ng-bootstrap · GitHub
popper.min.jsをダウンロードする方法 - ITを分かりやすく解説
npm install WARN deprecated popper.js@1.16.1: You can find the new Popper v2 at @popperjs/core, this package is dedicated to the legacy v1 · Issue #111 · creativetimofficial/material-dashboard · GitHub