react-app-polyfill only "starts"/activates when running local development mode on Windows

[mwallace72]

We have an application that is a long-ejected CRA. It utilizes react-app-polyfill for IE11 compatibility.

We've noticed that the polyfills for ie11 are only "on" during local development mode (npm start) when the machine executing the command is Windows.
We discovered this by trying to start the app on a Mac, then use Browserstack's Local Testing feature to view the localhost app in IE11.

When we start the app locally on Windows and run Browserstack Local Testing in the Windows machine, it works great.
When we start the app locally on Mac and run Browserstack Local Testing in the Mac machine, the console shows errors that we solved with polyfill already.

Anyone know if we can force it on for any originating OS? We would really like to be able to use Macs with Browserstack to do IE11 local testing.