Action cameras (and many others) will encode MP4 video using H.264 or using constant rate H.265. This is somewhat space intensive though, so taking lots of video can quickly fill up your disks. A fix for this it to re-encode as H.265 or to switch from constant bitrate to a constant rate factor (i.e. quality level). These are much more space efficient algorithms with no perceptible drop in quality. If your goal is to have the best video you can while reducing file sizes, this is a good approach.

If you look up MTP transfer on MacOS, you’ll likely come across OpenMTP or MTP For Mac. If you want something basic and included, then MacOS comes with Image Capture. No features really, just copy and delete, but sometimes basic is all we actually need. For the GoPro, go into settings and set USB to MTP mode and it should show up in Finder. From there, it’s easy to copy and/or delete photos