Recommendation to merge gopro clips

What is the best way to combine all of the GoPro segments into 1 single video? We then can stitch the resulting lef & right videos? I currently use Quicktime to merge all of the first half left then clips but it degrade the original image.

There is no need to combine video segments first. With the control key on Windows or the command key on macOS, you can select multiple files in the video selection dialog and then ActionStitch can handle them as if they were a single file.