Because they are no longer bundled, you must source the files separately if you want the classic Bootstrap 3 look.
GitHub - Darkseal/bootstrap4-glyphicons: How use Glyphicons with Bootstrap 4 (without getting mad) glyphicon bootstrap 4 download
If you are looking to download for Bootstrap 4 , it is important to note that Glyphicons were officially dropped from the core Bootstrap framework starting with version 4.0. Unlike Bootstrap 3, which included them by default, Bootstrap 4 was built to be more lightweight and allows developers to choose their own icon libraries. Because they are no longer bundled, you must
However, you can still use Glyphicons in Bootstrap 4 by manually adding them or, more commonly, switching to a modern alternative. 1. How to "Download" and Use Glyphicons in Bootstrap 4 Because they are no longer bundled