Increase the quality of the screen recorder in iOS
You aren't missing anything. There are no settings whatsoever that you can change to customize the capture characteristics of the built-in iOS screen recorder.


How to record the screen on your iPhone, iPad, or iPod touch


However, a simple Web search reveals a bunch of 3rd party iOS/macOS/Windows screen recording apps that you can try out to see if they offer better quality/cutomizations.


https://filmora.wondershare.com/screen-recorder/best-ios-screen-recorder.html
https://www.aiseesoft.com/screen-recorder/iphone-screen-recorder-app.html
https://itunes.apple.com/app/techsmith-capture/id1266321056
https://iphonebyte.com/iphone-screen-recorder-apps/