Ah, I’m using bootstrap 4, which has css and scss, they dropped less support a couple of years ago when they released version 4
https://npmfs.com/package/bootstrap/4.4.1/
If you’re still on Bootstrap 2 or 3, you can do the same, but with the less compiler.
Nope, sass and less both treat @import for files ending in .css as literal css imports and won’t import the file.
After quickly checking the docs for less, it does look like you can over-write that behaviour by forcing less to import it as a less file with @import (less) "{}/node_modules/bootstrap/dist/bootstrap.css", which means it will get compiled.