HEVC - GoPro Videos
GoPro uses the H.265 standard for High Quality videos.
Video files are recorded using the h.264 codec and the MP4 file type, the exception being some resolution/frame rate combinations on the HERO6 and HERO7 Black.
HEVC Format
The GoPro uses High Efficiency Video Coding (H.265) to capture videos - especially at hight frame rates for 4k at 60fps and 1080p at 240 fps. This is the latest video coding, and not supported by older computer systems - thankfully this has been around for a while
The HEVC standard allows the ability to store high quality video without using a lot of disk space. In fact videos compressed with H.265 standard uses up to 40 percent less space without sacrificing quality.
GoPro started using HEVC in the GoPro Hero 5 series.
Apple Users
If your computer is not running MacOS 10.13+ (MacOS High Sierra or macOS Mojave), your not able to view the videos on your computer. The H.265 standard requires at least the A10 chip. If your computer isn't eligible for the High Sierra, then your computer doesn't have the A10 chip.
iPhone 7+ users have support for the HEVC standard.
Windows Computers
If your computer is running Windows 10, then you have the proper hardware to view the GoPro videos.
Older Systems
If you don't have the hardware to support the videos, you can always upload them to Google Photos and have the videos be translated. Google Photos has supported HEVC video since September 2017.