Go to DJI Flight Log Viewer | Phantom Help
Follow the instructions there to upload your flight record from your phone or tablet.
That will give you a detailed report on the flight data.
On the far left under the map window, look for the Download...
I put some image pairs to compare the high and low resolution options over here:
https://mavicpilots.com/threads/comparison-images-high-res-vs-native-res.152237/post-1707297
I shot a few pairs of images in the (low) native resolution and the high resolution for comparison.
https://drive.google.com/drive/folders/1wvoqYiUZTLKBYf5rn0UsQFFsl7OfdupI?usp=sharing
Sounds like you were expecting the old original RTH method.
DJI has advanced and now offers other RTH methods as well.
Read about them from p50 in the manual here...