There are apps that use additional processes for GPU acceleration (i.e. Microsoft Teams, Slack, Chrome) where this script doesn't really help. It is however pretty easy to fix this, as these processes are usually contained within <something GPU Helper>.app files, so it's just a matter of selecting these too.

As an example, Google Chrome uses an additional GPU Helper process:

Setting the checkbox Prefer external GPU for just the Google Chrome.app does not do the trick, because the actual GPU acceleration is ran by the other process. What has worked for me was manually changing that process' checkbox for external GPU preference. Having tested it with other apps, all of these seem to follow the pattern bellow:

Essentially, it's a matter of getting into the application's contents folder and scanning for *.app files.

I would be happy to work on this when I have time, but that might not be for a while. Given how simple this is I would be happy for someone else to take over, should they have the time.