This repo shows, that using the module entry in package.json doesn't have any negative impacts when using Next.js. It builds just fine, transforms ES6 to ES5 & runs in IE11 with absolutely no problems.
Website compiles perfectly to ES5, the only change i had to do was remove the require('tslib'); line, and everything works perfectly.
nextjs-blog contains the starter tutorial of Next.js and browser folder contains the built @simplewebauthn/browser, and is imported using relative file import "npm install file:../browser"