Unfortunately, it isn’t possible to add an exception for the homepage directly in the plugin settings.
However, I created a small plugin that you can install alongside the Simple Website Redirect plugin to prevent the homepage from redirecting.
You can view the code here:
https://gist.github.com/wpscholar/c65523da12007c55962743bbd8eea1d9
Click the “Download Zip” button in the top right to download the plugin.
To install, you’ll have to visit the “Plugins” -> “Add New” page in WordPress and then click “Upload Plugin”. Click “Choose File”, select the downloaded .zip file from your computer, then click “Install Now”. Be sure to activate it on the next screen.
Once installed, it should work by default. Keep in mind if you’ve already implemented a permanent redirect, the homepage may still redirect for you until you clear your browser cache. (See https://wpscholar.com/blog/browser-caching-301-redirects/). The best way to test redirects is by using a fresh Chrome incognito window.